White House: Syria crosses ‘red line’ with use of chemical weapons on its people

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.

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.

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.

A man walks amid debris and dust on January 31.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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