White House: Syria crosses 'red line' with use of chemical weapons

In this photo provided by the anti-government activist group Aleppo Media Center, Syrian men help survivors out of a building in Aleppo after it was bombed, allegedly by a Syrian regime warplane on Saturday, February 8. The United Nations estimates more than 100,000 people have been killed since the Syrian conflict began in March 2011. Click through to see the most compelling images taken during the conflict, which is now a civil war:

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Syrian civil war in photos —

In this photo provided by the anti-government activist group Aleppo Media Center, Syrian men help survivors out of a building in Aleppo after it was bombed, allegedly by a Syrian regime warplane on Saturday, February 8. The United Nations estimates more than 100,000 people have been killed since the Syrian conflict began in March 2011. Click through to see the most compelling images taken during the conflict, which is now a civil war:

Syrians gather at a site hit by barrel bombs, allegedly dropped by a regime helicopter on the opposition-controlled Mesekin Hananu district of Aleppo on February 8.

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Syrians gather at a site hit by barrel bombs, allegedly dropped by a regime helicopter on the opposition-controlled Mesekin Hananu district of Aleppo on February 8.

Civilians wave national flags as they take part in a rally in support of Syrian President Bashar al-Assad in Damascus, in a handout photo released by the official Syrian Arab News Agency on February 8.

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Civilians wave national flags as they take part in a rally in support of Syrian President Bashar al-Assad in Damascus, in a handout photo released by the official Syrian Arab News Agency on February 8.

A man stands next to debris in the road following a reported airstrike by Syrian government forces in the northern city of Aleppo on February 8.

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MOHAMMED WESAM/AFP/Getty Images

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A man stands next to debris in the road following a reported airstrike by Syrian government forces in the northern city of Aleppo on February 8.

Medical personnel look for survivors after a reported airstrike in Aleppo, Syria, on Saturday, February 1.

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MOHAMMED AL-KHATIEB/AFP/Getty Images

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Medical personnel look for survivors after a reported airstrike in Aleppo, Syria, on Saturday, February 1.

Syrians carry a dead body following an airstrike on February 1.

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Syrians carry a dead body following an airstrike on February 1.

A man walks amid debris and dust on January 31.

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A man walks amid debris and dust on January 31.

An injured man is covered in dust after an airstrike on January 29.

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MOHAMMED AL-KHATIEB/AFP/Getty Images

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An injured man is covered in dust after an airstrike on January 29.

A man tries to fix electrical wires in a neighborhood of Aleppo, Syria, on January 27.

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STRinger/AFP/Getty Images

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A man tries to fix electrical wires in a neighborhood of Aleppo, Syria, on January 27.

Rebels and civilians check out a crater that activists say resulted from a Syrian government airstrike on an Aleppo bus station on Tuesday, January 21.

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Rebels and civilians check out a crater that activists say resulted from a Syrian government airstrike on an Aleppo bus station on Tuesday, January 21.

Men rush to a site that Syrian government forces reportedly hit in Aleppo on January 21.

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Men rush to a site that Syrian government forces reportedly hit in Aleppo on January 21.

Buildings lie in ruins in Aleppo on Sunday, January 19, after reported air raids by Syrian government planes.

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MOHAMMED WESAM/AFP/Getty Images

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Buildings lie in ruins in Aleppo on Sunday, January 19, after reported air raids by Syrian government planes.

A Syrian child collects items from a garbage pile on Saturday, January 18, in Douma, northeast of the capital.

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A Syrian child collects items from a garbage pile on Saturday, January 18, in Douma, northeast of the capital.

A piece of exploded mortar lies in a street in Daraya, a city southwest of Damascus, on Friday, January 17.

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A piece of exploded mortar lies in a street in Daraya, a city southwest of Damascus, on Friday, January 17.

Residents search for survivors in Aleppo on Saturday, December 28, 2013, after what activists said were airstrikes by forces loyal to Syrian President Bashar al-Assad.

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STRINGER/reuters/LANDOV

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Residents search for survivors in Aleppo on Saturday, December 28, 2013, after what activists said were airstrikes by forces loyal to Syrian President Bashar al-Assad.

A man appears distraught after an air raid in Aleppo on Monday, December 23.

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A man appears distraught after an air raid in Aleppo on Monday, December 23.

Free Syrian Army fighters sit in a damaged house in Old Aleppo on Saturday, December 21.

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Abdalrhman Ismail/Reuters/Stringer/Landov

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Free Syrian Army fighters sit in a damaged house in Old Aleppo on Saturday, December 21.

People search for survivors amid the rubble after an airstrike in Aleppo on Tuesday, December 17.

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MOHAMMED AL-KHATIEB/AFP/Getty Images

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People search for survivors amid the rubble after an airstrike in Aleppo on Tuesday, December 17.

A man sits on the ground after the airstrike in Aleppo on December 17.

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MOHAMMED AL-KHATIEB/AFP/Getty Images

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A man sits on the ground after the airstrike in Aleppo on December 17.

A woman carries children following airstrikes on a rebel area of Aleppo on Sunday, December 15.

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MOHAMMED AL-KHATIEB/AFP/Getty Images

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A woman carries children following airstrikes on a rebel area of Aleppo on Sunday, December 15.

Syrians look at the aftermath of an airstrike on a rebel area of Aleppo on December 15.

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MOHAMMED AL-KHATIEB/AFP/Getty Images

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Syrians look at the aftermath of an airstrike on a rebel area of Aleppo on December 15.

Syrians help a wounded woman following airstrikes in Aleppo on December 15.

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Syrians help a wounded woman following airstrikes in Aleppo on December 15.

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Syrians look at the aftermath of an airstrike on a rebel area of Aleppo on December 15.

Syrian rebel fighters clash with pro-government forces in Aleppo on Wednesday, December 11.

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Syrian rebel fighters clash with pro-government forces in Aleppo on Wednesday, December 11.

A woman weeps inside a damaged vehicle after forces loyal to President Bashar al-Assad captured the town of Nabak on Monday, December 9.

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A woman weeps inside a damaged vehicle after forces loyal to President Bashar al-Assad captured the town of Nabak on Monday, December 9.

A rebel fighter takes position during fighting with government forces in Deir Ezzor on Monday, December 2.

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A rebel fighter takes position during fighting with government forces in Deir Ezzor on Monday, December 2.

Shiite fighters from a group called the Hussein Brigade search for rebels from the Free Syrian Army in Hejeira on Thursday, November 21.

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Jaber al-Helo/AP

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Shiite fighters from a group called the Hussein Brigade search for rebels from the Free Syrian Army in Hejeira on Thursday, November 21.

Free Syrian Army rebels battle government forces in Aleppo on Monday, November 18.

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KARAM AL-MASRI/AFP/Getty Images

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Free Syrian Army rebels battle government forces in Aleppo on Monday, November 18.

A rebel fighter holds his position in a damaged building during clashes with government forces in Deir Ezzor on Monday, November 11.

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AHMAD ABOUD/AFP/Getty Images

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A rebel fighter holds his position in a damaged building during clashes with government forces in Deir Ezzor on Monday, November 11.

A rebel fighter fires during clashes with government forces in Deir Ezzor on November 11.

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AHMAD ABOUD/AFP/Getty Images

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A rebel fighter fires during clashes with government forces in Deir Ezzor on November 11.

A rebel fighter prepares an improvised mortar shell in Aleppo, Syria, on Saturday, November 9.

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FOUAD HALLAK/AFP/Getty Images

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A rebel fighter prepares an improvised mortar shell in Aleppo, Syria, on Saturday, November 9.

Two injured men are transported on a cart in Aleppo, Syria, following shelling as fighting between pro-government forces and rebels continues on Saturday, October 26.

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KARAM AL-MASRI/AFP/Getty Images

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Two injured men are transported on a cart in Aleppo, Syria, following shelling as fighting between pro-government forces and rebels continues on Saturday, October 26.

Rebel fighters hold a position in Deir Ezzor, Syria, on Thursday, October 24.

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Rebel fighters hold a position in Deir Ezzor, Syria, on Thursday, October 24.

An opposition fighter stands in the doorway of a building as he smokes a cigarette in Deir Ezzor, Syria, on Tuesday, October 22.

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An opposition fighter stands in the doorway of a building as he smokes a cigarette in Deir Ezzor, Syria, on Tuesday, October 22.

People use buckets as they try to extinguish a fire that ignited at a fuel station in Aleppo, Syria, on Sunday, October 20.

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KARAM AL-MASRI/AFP/Getty Images

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People use buckets as they try to extinguish a fire that ignited at a fuel station in Aleppo, Syria, on Sunday, October 20.

A Syrian opposition fighter aims a catapult toward regime forces in Aleppo, Syria, on Thursday, October 17.

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KARAM AL-MASRI/AFP/Getty Images

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A Syrian opposition fighter aims a catapult toward regime forces in Aleppo, Syria, on Thursday, October 17.

Firefighters extinguish a burning vehicle after two mortar rounds struck the Abu Roumaneh area in Damascus, Syria, on Saturday, October 12.

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ap

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Firefighters extinguish a burning vehicle after two mortar rounds struck the Abu Roumaneh area in Damascus, Syria, on Saturday, October 12.

An opposition fighter aims as others run for cover while they hold a position behind burning tires in the Salaheddin district of the northern Syrian city of Aleppo on Wednesday, October 9.

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TAREK ABU Al-FAHEM/AFP/Getty Images

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An opposition fighter aims as others run for cover while they hold a position behind burning tires in the Salaheddin district of the northern Syrian city of Aleppo on Wednesday, October 9.

An opposition fighter smokes a cigarette as he takes a break following the injury of his friend in the Salaheddin neighborhood of Aleppo on October 9.

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KARAM AL-MASRI/AFP/Getty Images

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An opposition fighter smokes a cigarette as he takes a break following the injury of his friend in the Salaheddin neighborhood of Aleppo on October 9.

Smoke rises after a mortar shell hit a residential area during fighting between Syrian government forces and rebels in Maaret al-Numan, Syria, on October, 9.

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AP

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Smoke rises after a mortar shell hit a residential area during fighting between Syrian government forces and rebels in Maaret al-Numan, Syria, on October, 9.

Rebel fighters cover a car in mud for camouflage at an undisclosed location in Syria's northwestern province of Idlib on Tuesday, October 8.

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MOHAMAD JADAAN/AFP/Getty Images

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Rebel fighters cover a car in mud for camouflage at an undisclosed location in Syria's northwestern province of Idlib on Tuesday, October 8.

Masked female rebel fighters walk alongside their trainer on a street in the Salaheddin district of Aleppo, Syria, on October 8.

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KARAM AL-MASRI/AFP/Getty Images

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Masked female rebel fighters walk alongside their trainer on a street in the Salaheddin district of Aleppo, Syria, on October 8.

A rebel fighter prays moments before heading into battle in Maaret al-Numan, Syria, on Monday, October 7.

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AP

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A rebel fighter prays moments before heading into battle in Maaret al-Numan, Syria, on Monday, October 7.

A mother comforts her baby in an area where she and her family have taken shelter after fleeing their village turned battlefield in Syria's Idlib province on Sunday, September 22.

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A mother comforts her baby in an area where she and her family have taken shelter after fleeing their village turned battlefield in Syria's Idlib province on Sunday, September 22.

A man checks an AK-47 at his gun shop in Aleppo, Syria, on Saturday, September 21.

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JM LOPEZ/AFP/Getty Images

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A man checks an AK-47 at his gun shop in Aleppo, Syria, on Saturday, September 21.

Free Syrian Army fighters take cover moments after firing a rocket toward government forces in the Idlib province of northern Syria on Friday, September 20.

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AP

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Free Syrian Army fighters take cover moments after firing a rocket toward government forces in the Idlib province of northern Syria on Friday, September 20.

Rebel fighters inspect a stairwell amid fighting against Syrian government forces on Thursday, September 19, in the Saif al-Dawla district of Aleppo, Syria.

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JM LOPEZ/AFP/Getty Images

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Rebel fighters inspect a stairwell amid fighting against Syrian government forces on Thursday, September 19, in the Saif al-Dawla district of Aleppo, Syria.

A Syrian child sits in a village in the Idlib province countryside on September 19.

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AP

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A Syrian child sits in a village in the Idlib province countryside on September 19.

Opposition fighters react after returning from the battlefield in the Idlib province countryside on September 19.

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Opposition fighters react after returning from the battlefield in the Idlib province countryside on September 19.

Smoke rises after a bomb was thrown from a helicopter, hitting a rebel position during heavy fighting between troops loyal to Syrian President Bashar al-Assad and opposition fighters in the Idlib province on September 19.

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ap

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Smoke rises after a bomb was thrown from a helicopter, hitting a rebel position during heavy fighting between troops loyal to Syrian President Bashar al-Assad and opposition fighters in the Idlib province on September 19.

Rebel fighters duck behind a barricade from firing in Aleppo on Wednesday, September 18.

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JM LOPEZ/AFP/Getty Images

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Rebel fighters duck behind a barricade from firing in Aleppo on Wednesday, September 18.

AFP reporter Sammy Ketz hits the ground as a Syrian soldier runs past during sniper fire in Maalula on September 18. Ketz and a photographer were reporting on the ancient Christian Syrian town northeast of Damascus.

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AFP reporter Sammy Ketz hits the ground as a Syrian soldier runs past during sniper fire in Maalula on September 18. Ketz and a photographer were reporting on the ancient Christian Syrian town northeast of Damascus.

A Syrian opposition fighter takes a break on a mountain near a rebel camp in Idlib province on September 18.

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A Syrian opposition fighter takes a break on a mountain near a rebel camp in Idlib province on September 18.

A Free Syrian Army fighter rests inside a cave at a rebel camp in Idlib province on Tuesday, September 17.

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Narciso Contreras/AP

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A Free Syrian Army fighter rests inside a cave at a rebel camp in Idlib province on Tuesday, September 17.

Volunteers wear protective gear to show a class how to respond to a chemical attack in Aleppo, Syria, on September 15. For two months, Mohammad Zayed, an Aleppo University student, has been training a group of 26 civilians to respond to a chemical attack.

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JM LOPEZ/AFP/Getty Images

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Volunteers wear protective gear to show a class how to respond to a chemical attack in Aleppo, Syria, on September 15. For two months, Mohammad Zayed, an Aleppo University student, has been training a group of 26 civilians to respond to a chemical attack.

Syria's pro-Assad militia rest near Maalula, Syria, on Friday, September 13.

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POCHUYEV MIKHAIL/ITAR-TASS /Landov

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Syria's pro-Assad militia rest near Maalula, Syria, on Friday, September 13.

Syrian soldiers take aim at rebel fighters positioned in the mountains of the Christian town of Maalula on September 13.

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Stringer/AFP/Getty Images

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Syrian soldiers take aim at rebel fighters positioned in the mountains of the Christian town of Maalula on September 13.

Rebels parade at a former military academy north of Aleppo during a September 13 ceremony to mark an agreement to unite two rebel brigade forces.

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JM LOPEZ/AFP/Getty Images

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Rebels parade at a former military academy north of Aleppo during a September 13 ceremony to mark an agreement to unite two rebel brigade forces.

A fighter of the Popular Front for the Liberation of Palestine General Command squats next to the covered body of an alleged foreign rebel fighter in the Yarmouk refugee camp in the Syrian capital of Damascus on Thursday, September 12.

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ANWAR AMRO/AFP/Getty Images

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A fighter of the Popular Front for the Liberation of Palestine General Command squats next to the covered body of an alleged foreign rebel fighter in the Yarmouk refugee camp in the Syrian capital of Damascus on Thursday, September 12.

An opposition fighter runs in front of a sniper curtain in the industrial area of Deir Ezzor, Syria, during clashes with regime forces on September 12.

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ABO SHUJA/AFP/Getty Images

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An opposition fighter runs in front of a sniper curtain in the industrial area of Deir Ezzor, Syria, during clashes with regime forces on September 12.

A sheet hangs across an alley way to shield fighters from sniper fire as a fighter of the Popular Front for the Liberation of Palestine General Command walks past destroyed buildings in the Yarmouk refugee camp in Damascus, Syria, on September 12.

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ANWAR AMRO/AFP/Getty Images

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A sheet hangs across an alley way to shield fighters from sniper fire as a fighter of the Popular Front for the Liberation of Palestine General Command walks past destroyed buildings in the Yarmouk refugee camp in Damascus, Syria, on September 12.

A Free Syrian Army fighter stands guard inside a damaged house in Aleppo's Qastal al-Harami neighborhood on September 11.

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Nour Kelze/Reuters/Stringer/Landov

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A Free Syrian Army fighter stands guard inside a damaged house in Aleppo's Qastal al-Harami neighborhood on September 11.

Free Syrian Army fighters climb a flight of stairs to take positions near the Hanano barracks on September 11.

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Muzaffar Salman/Reuters/Landov

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Free Syrian Army fighters climb a flight of stairs to take positions near the Hanano barracks on September 11.

A Syrian government tank is seen during clashes with Free Syrian Army fighters in Maaloula, Syria, on September 11.

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SANA/ap

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A Syrian government tank is seen during clashes with Free Syrian Army fighters in Maaloula, Syria, on September 11.

A funeral is held on September 11 for three Christian Syrians killed during battles with an al Qaeda-linked rebel group that took control of the historic Christian town of Maaloula from regime forces during the weekend.

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ANWAR AMRO/AFP/Getty Images

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A funeral is held on September 11 for three Christian Syrians killed during battles with an al Qaeda-linked rebel group that took control of the historic Christian town of Maaloula from regime forces during the weekend.

A man walks through a destroyed residential area of Saraqib, Syria, on Monday, September 9, following repeated airstrikes by government forces.

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GIOVANNI DIFFIDENTI/AFP/Getty Images

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A man walks through a destroyed residential area of Saraqib, Syria, on Monday, September 9, following repeated airstrikes by government forces.

A soldier wears a picture of Syrian President Bashar al-Assad on his chest while at a market in old Damascus on September 8.

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KHALED AL-HARIRI/REUTERS/LANDOV

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A soldier wears a picture of Syrian President Bashar al-Assad on his chest while at a market in old Damascus on September 8.

A Free Syrian Army fighter prays in a trench in the Damascus suburbs on September 8.

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Raje Alsori/REUTERS/LANDOV

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A Free Syrian Army fighter prays in a trench in the Damascus suburbs on September 8.

A Free Syrian Army fighter takes up a shooting position in Aleppo on September 8.

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Hamid Khatib/REUTERS/LANDOV

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A Free Syrian Army fighter takes up a shooting position in Aleppo on September 8.

A Free Syrian Army fighter runs for cover in Raqqa province on September 8.

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Nour Fourat/REUTERS/LANDOV

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A Free Syrian Army fighter runs for cover in Raqqa province on September 8.

Buildings are heavily damaged in the Salah al-Din area of Aleppo on September 8.

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ABO MHIO/AFP/Getty Images

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Buildings are heavily damaged in the Salah al-Din area of Aleppo on September 8.

<a href="http://www.cnn.com/2013/09/09/world/gallery/issa-syria/index.html" target="_blank">A boy named Issa</a>, 10, carries a mortar shell in a weapons factory of the Free Syrian Army in Aleppo on Saturday, September 7. The boy works with his father in the factory.

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A boy named Issa, 10, carries a mortar shell in a weapons factory of the Free Syrian Army in Aleppo on Saturday, September 7. The boy works with his father in the factory.

Issa fixes a mortar launcher in the Aleppo weapons factory on September 7.

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Issa fixes a mortar launcher in the Aleppo weapons factory on September 7.

A bedroom lies in ruins after clashes between government forces and rebels around Ariha on September 7.

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Houssam Abo Dabak/REUTERS/LANDOV

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A bedroom lies in ruins after clashes between government forces and rebels around Ariha on September 7.

Syrian forces are seen in the Syrian Christian town of Maaloula on September 7.

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Syrian forces are seen in the Syrian Christian town of Maaloula on September 7.

A Syrian soldier prepares large-caliber bullets for a machine gun in Maaloula on September 7.

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stringer/AFP/Getty images

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A Syrian soldier prepares large-caliber bullets for a machine gun in Maaloula on September 7.

A man stands inside a home damaged by heavy shelling in Arbeen, a suburb of Damascus, Syria, on September 7.

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A man stands inside a home damaged by heavy shelling in Arbeen, a suburb of Damascus, Syria, on September 7.

Men gather on the remains of a destroyed building after reported airstrikes by Syrian government forces in the rebel-held northwestern Syrian province of Idlib on Thursday, September 5.

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ABU AMAR AL-TAFTANAZ/AFP/Getty Image

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Men gather on the remains of a destroyed building after reported airstrikes by Syrian government forces in the rebel-held northwestern Syrian province of Idlib on Thursday, September 5.

A Free Syrian Army fighter takes cover as he watches forces loyal to President Bashar al-Assad near Hanano barracks in Aleppo on September 3.

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Hamid Khatib/Reuters/Stringer/Landov

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A Free Syrian Army fighter takes cover as he watches forces loyal to President Bashar al-Assad near Hanano barracks in Aleppo on September 3.

Free Syrian Army fighters walk inside a damaged house in Aleppo on September 3.

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Hamid Khatib/Reuters/Stringer/Landov

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Free Syrian Army fighters walk inside a damaged house in Aleppo on September 3.

Free Syrian Army fighters talk inside a burnt house in Aleppo on September 3.

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Hamid Khatib/Reuters/Stringer/Landov

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Free Syrian Army fighters talk inside a burnt house in Aleppo on September 3.

A Free Syrian Army fighter peeks through the curtains of a bedroom in Deir ez-Zor, Syria, on Monday, September 2.

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Khalil Ashawi/Reuters/Stringer/Landov

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A Free Syrian Army fighter peeks through the curtains of a bedroom in Deir ez-Zor, Syria, on Monday, September 2.

Free Syrian Army fighters take their positions behind piled sandbags, as one of them points his weapon, in Deir ez-Zor on September 2.

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Khalil Ashawi/Reuters/Stringer/Landov

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Free Syrian Army fighters take their positions behind piled sandbags, as one of them points his weapon, in Deir ez-Zor on September 2.

A rebel fighter points his weapon at Syrian regime forces in Deir ez-Zor on September 2.

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ABO SHUJA/AFP/Getty Images

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A rebel fighter points his weapon at Syrian regime forces in Deir ez-Zor on September 2.

Syrian firefighters try to extinguish a fire after a missile hit a residential building in Damascus, Syria, on September 2.

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SANA/AP

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Syrian firefighters try to extinguish a fire after a missile hit a residential building in Damascus, Syria, on September 2.

A U.N. arms expert collects samples during an inspection of a suspected chemical weapons strike site in the Ghouta area outside Damascus on August 29.

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Ammar al-Arbini/AFP/Getty Images

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A U.N. arms expert collects samples during an inspection of a suspected chemical weapons strike site in the Ghouta area outside Damascus on August 29.

People search for belongings in rubble in Raqqa, Syria, on August 29.

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STRINGER/Reuters/LANDOV

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People search for belongings in rubble in Raqqa, Syria, on August 29.

Free Syrian Army fighters launch a rocket toward forces loyal to Syrian President Bashar al-Assad in Deir Ezzor on August 29.

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Khalil Ashawi/reuters/landov

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Free Syrian Army fighters launch a rocket toward forces loyal to Syrian President Bashar al-Assad in Deir Ezzor on August 29.

A Syrian Kurd uses hay to hide another woman in a training session organized by the Kurdish Women's Defense Units on Wednesday, August 28, in a northern Syrian border village. They're preparing if the area comes under attack.

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BENJAMIN HILLER/AFP/Getty Images

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A Syrian Kurd uses hay to hide another woman in a training session organized by the Kurdish Women's Defense Units on Wednesday, August 28, in a northern Syrian border village. They're preparing if the area comes under attack.

Free Syrian Army fighters escort U.N. vehicles with chemical weapons experts on August 28 through a site of a suspected chemical weapons attack outside Damascus.

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Bassam Khabieh/REUTERS/landov

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Free Syrian Army fighters escort U.N. vehicles with chemical weapons experts on August 28 through a site of a suspected chemical weapons attack outside Damascus.

A Free Syrian Army fighter takes position behind sandbags in the old city of Aleppo, Syria, on Tuesday, August 27.

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Stringer/reuters/landov

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A Free Syrian Army fighter takes position behind sandbags in the old city of Aleppo, Syria, on Tuesday, August 27.

A U.N. team leaves its Damascus, Syria, hotel in a convoy on Monday, August 26. The team was to investigate an alleged chemical attack that killed hundreds last week in a suburb of the Syrian capital. Sniper fire hit a vehicle used by the U.N. chemical weapons investigation team multiple times Monday, according to the United Nations.

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Stringer/AP

Syrian civil war in photos —

A U.N. team leaves its Damascus, Syria, hotel in a convoy on Monday, August 26. The team was to investigate an alleged chemical attack that killed hundreds last week in a suburb of the Syrian capital. Sniper fire hit a vehicle used by the U.N. chemical weapons investigation team multiple times Monday, according to the United Nations.

A Syrian soldier walks down a street in Damascus on Saturday, August 24.

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A Syrian soldier walks down a street in Damascus on Saturday, August 24.

Pigeons lie dead on the ground on August 24 from after what activists say is the use of chemical weapons by government forces in the Damascus suburb of Arbeen.

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STRINGER/reuters/LANDOV

Syrian civil war in photos —

Pigeons lie dead on the ground on August 24 from after what activists say is the use of chemical weapons by government forces in the Damascus suburb of Arbeen.

Columns of smoke rise in Barzeh after heavy shelling on Friday, August 23.

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Hassan Ammar/AP

Syrian civil war in photos —

Columns of smoke rise in Barzeh after heavy shelling on Friday, August 23.

A young Free Syrian Army fighter is reflected in a mirror as he takes position in a house in Aleppo on Thursday, August 22.

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MUZAFFAR SALMAN/reuters/LANDOV

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A young Free Syrian Army fighter is reflected in a mirror as he takes position in a house in Aleppo on Thursday, August 22.

Rebels move around a building in Aleppo on August 22.

Photos: Unrest in Syria

MUZAFFAR SALMAN/reuters/LANDOV

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Rebels move around a building in Aleppo on August 22.

Syrian rebels claim pro-government forces used chemical weapons to kill citizens outside Damascus on Wednesday, August 21. People inspect bodies in this photo released by the Syrian opposition Shaam News Network.

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Syrian rebels claim pro-government forces used chemical weapons to kill citizens outside Damascus on Wednesday, August 21. People inspect bodies in this photo released by the Syrian opposition Shaam News Network.

People search the rubble of a bombed building in Aleppo, Syria, on Friday, August 16.

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People search the rubble of a bombed building in Aleppo, Syria, on Friday, August 16.

Men bury the bodies of six members of the same family killed in a bombing in Raqqa on Saturday, August 10.

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Syrian civil war in photos —

Men bury the bodies of six members of the same family killed in a bombing in Raqqa on Saturday, August 10.

Syrian Army soldiers patrol a devastated street in Homs on Wednesday, July 31.

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Syrian Army soldiers patrol a devastated street in Homs on Wednesday, July 31.

Free Syrian Army fighters move through a hole in a wall in Khan al-Assal on Monday, July 22, after seizing the town.

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Hamid Khatib/reuters/LANDOv

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Free Syrian Army fighters move through a hole in a wall in Khan al-Assal on Monday, July 22, after seizing the town.

A rebel fighter walks past swings in a deserted playground in Deir al-Zor, Syria, on Sunday, July 21.

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A rebel fighter walks past swings in a deserted playground in Deir al-Zor, Syria, on Sunday, July 21.

A rebel fighter speaks with a fellow fighter through a hole in a wall in Deir al-Zor on July 21.

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A rebel fighter speaks with a fellow fighter through a hole in a wall in Deir al-Zor on July 21.

A Free Syrian Army fighter casts a shadow on a wall as he carries his weapon in a shelter in Deir al-Zor on Thursday, July 18.

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Khalil Ashawi/Reuters/Landov

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A Free Syrian Army fighter casts a shadow on a wall as he carries his weapon in a shelter in Deir al-Zor on Thursday, July 18.

Yahya Sweed, 13, is comforted by his father as he lies on a bed in Kfar Nubul on Tuesday, July 16. The boy was injured by shrapnel, resulting in the amputation of his right leg.

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DANIEL LEAL-OLIVAS/AFP/Getty Images

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Yahya Sweed, 13, is comforted by his father as he lies on a bed in Kfar Nubul on Tuesday, July 16. The boy was injured by shrapnel, resulting in the amputation of his right leg.

A rebel fighter naps in a trench about 300 feet from the Syrian government forces' positions along the highway connecting Idlib with Latakia on Monday, July 15.

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DANIEL LEAL OLIVAS/AFP/Getty Images

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A rebel fighter naps in a trench about 300 feet from the Syrian government forces' positions along the highway connecting Idlib with Latakia on Monday, July 15.

A rebel fighter uses a hole in the wall of a destroyed school to aim at Syrian government forces in the Izaa district of Aleppo on Sunday, July 14.

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A rebel fighter uses a hole in the wall of a destroyed school to aim at Syrian government forces in the Izaa district of Aleppo on Sunday, July 14.

A Free Syrian Army fighter uses a mirror to scope out snipers loyal to Syrian President Bashar al-Assad in Aleppo on Friday, July 12.

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MUZAFFAR SALMAN/reuters/LANDOv

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A Free Syrian Army fighter uses a mirror to scope out snipers loyal to Syrian President Bashar al-Assad in Aleppo on Friday, July 12.

A Free Syrian Army fighter stands over a boy who was injured during shelling in Al-Bara on Monday, July 8.

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DANIEL LEAL-OLIVAS/AFP/Getty Images

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A Free Syrian Army fighter stands over a boy who was injured during shelling in Al-Bara on Monday, July 8.

Members of the Free Syrian Army fire a homemade rocket toward regime forces in Deir al-Zor on Sunday, June 16.

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STRINGER/Reuters/LANDOV

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Members of the Free Syrian Army fire a homemade rocket toward regime forces in Deir al-Zor on Sunday, June 16.

Syrian rebels leave their position in the northwestern town of Maaret al-Numan on Thursday, June 13. The White House said that <a href="http://www.cnn.com/2013/06/13/politics/syria-us-chemical-weapons/index.html">the Syrian government has crossed a "red line"</a> with its use of chemical weapons and announced it would start arming the rebels.

Photos: Unrest in Syria

DANIEL LEAL-OLIVAS/AFP/Getty Images

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Syrian rebels leave their position in the northwestern town of Maaret al-Numan on Thursday, June 13. The White House said that the Syrian government has crossed a "red line" with its use of chemical weapons and announced it would start arming the rebels.

Forces loyal to Syrian President Bashar al-Assad are seen near Qusayr on Thursday, May 30.

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Forces loyal to Syrian President Bashar al-Assad are seen near Qusayr on Thursday, May 30.

Syrian rebels take position in a house during clashes with regime forces in the old city of Aleppo on May 22.

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Syrian rebels take position in a house during clashes with regime forces in the old city of Aleppo on May 22.

Syrian army soldiers take control of the village of Western Dumayna north of the rebel-held city of Qusayr on Monday, May 13. Syrian troops captured three villages in Homs province, allowing them to cut supply lines to rebels inside Qusayr town, a military officer told AFP.

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JOSEPH EID/AFP/Getty Images

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Syrian army soldiers take control of the village of Western Dumayna north of the rebel-held city of Qusayr on Monday, May 13. Syrian troops captured three villages in Homs province, allowing them to cut supply lines to rebels inside Qusayr town, a military officer told AFP.

Rebel fighters fire at government forces in the northern Syrian city of Aleppo on Sunday, May 12.

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Rebel fighters fire at government forces in the northern Syrian city of Aleppo on Sunday, May 12.

Searchers use a flashlight as they look for survivors among the rubble created by what activists say was a missile attack from the Syrian regime, in Raqqa province, Syria, on April 25.

Photos: Unrest in Syria

Syrian civil war in photos —

Searchers use a flashlight as they look for survivors among the rubble created by what activists say was a missile attack from the Syrian regime, in Raqqa province, Syria, on April 25.

A Kurdish fighter from the "Popular Protection Units" (YPG) takes position inside a building in the majority-Kurdish Sheikh Maqsood area of Aleppo, on Apri. 21.

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MIGUEL MEDINA/AFP/Getty Images

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A Kurdish fighter from the "Popular Protection Units" (YPG) takes position inside a building in the majority-Kurdish Sheikh Maqsood area of Aleppo, on Apri. 21.

People walk past destroyed houses in the northern Syrian town of Azaz on Sunday, April 21.

Photos: Unrest in Syria

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People walk past destroyed houses in the northern Syrian town of Azaz on Sunday, April 21.

Free Syrian Army fighters take positions prior to an offensive against government forces in the Khan al-Assal area, near Aleppo on Saturday, April 20.

Photos: Unrest in Syria

ABDALGHNE KAROOF/REUTERS/LANDOV

Syrian civil war in photos —

Free Syrian Army fighters take positions prior to an offensive against government forces in the Khan al-Assal area, near Aleppo on Saturday, April 20.