STORY HIGHLIGHTS
- NEW: "Get the hell out now," Panetta advises al-Assad
- Rebels use seized army tanks to attack a military base, a commander says
- At least 85 people are killed in violence across Syria, opposition activists say
- Syria's top diplomat in London has left his post, according to British officials
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Northern Syria (CNN) -- Syrian rebel fighters fought to control a key road to the Turkish border and turned captured tanks against a government air base north of Syria's largest city on Monday.
The tanks came from the rebel seizure of an army outpost outside Aleppo, the scene of heavy fighting for more than a week. Rebel troops overran the outpost early Monday and were hauling out tank shells and crates of ammunition by afternoon.
The outpost was a restaurant outside the town of Anadan, about 10 kilometers (6 miles) north of Aleppo, that had been commandeered by government troops and surrounded by earthworks. Rebels were putting the captured armor to work Monday by shelling an air base outside Azaz, about 40 kilometers (25 miles) farther north, said Ahmed Afesh, a commander with the rebel Free Syrian Army.
Afesh showed off two Soviet-era T-55 tanks captured by his men Monday, as well as an armored personnel carrier and the smoldering wreckage of another destroyed during the fighting. Rebel fighters and civilians greeted him with handshakes and kisses.
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The rebels also have been able to establish growing enclaves in northern Syria and made attempts to seize a number of key border crossings last week. They already control much of the main western highway from Aleppo, Syria's commercial capital and largest city, to the Turkish border. And after the overnight battle outside the town of Anadan, traffic moved freely on a road that had been too dangerous for motorists days before.
Read more: Syria rebels appear more capable, yet still outgunned
But fighting continued inside Aleppo on Monday. U.N. observers reported the use of helicopters, tanks and artillery in the city, the head of the international monitoring mission, Lt. Gen. Babacar Gaye, said Monday. And opposition activists said government forces used helicopter gunships to launch rocket attacks on rebel fighters.
At least 85 people were killed across Syria on Monday, including 25 in Aleppo, according to the opposition Local Coordination Committees of Syria.
There were conflicting reports on who controlled the major Aleppo neighborhood of Salahuddin, which rebels had claimed days earlier. Both opposition fighters and the regime said they had taken over Salahuddin, where Al Jazeera correspondent Omar Khashram was wounded during heavy fighting Monday.
A cameraman and driver working with Khashram, who was being treated in a hospital in Turkey, told CNN that shrapnel from a shell penetrated gaps in the correspondent's flak jacket.
About 200,000 people in and around the city have fled shelling and heavy weapons fire in the past two days, Valerie Amos, the U.N. undersecretary-general for humanitarian affairs, said Sunday.
In several neighborhoods, those who remained were left without phone, Internet or electricity service as tanks shelled the city, according to Deama, an activist in the city. CNN isn't using her full name because disclosing it could put her in danger.
"We're afraid they are going to do something worse. Usually, they will cut off connections and isolate these neighborhoods more when they are about to make something worse," Deama said Monday.
Residents also faced bread and flour shortages, she said. Bakeries were shuttered.

Rebel fighters load an anti-aircraft machine gun on an armored vehicle in Atareb, east of Syria's second-largest city, Aleppo, on Tuesday, July 31. Unrest spread across other volatile regions of the country as forces of President Bashar al-Assad's regime shelled targets and launched raids in and around Damascus, Homs, Daraa and Deir Ezzor.
Syrian boys run near a building hit by bullets and fire in Atareb.
A member of the Free Syrian Army fires at forces loyal to President Bashar Al-Assad in a district of Aleppo called Salah Edinne on Tuesday.
A member of the Free Syrian Army carries an injured civilian to safety in Aleppo's district of Salah Edinne on Tuesday.
Members of the Free Syrian Army learn that a tank belonging to forces loyal to President Bashar Al-Assad is heading to the area.
A Syrian boy carries bags of bread as people wait outside a bakery near Syria's second-largest city, Aleppo.
A photo released by Syrian Arab News Agency depicts damaged buildings in Homs on Monday, July 30.
A Free Syrian Army fighter takes position Sunday, July 29, in Aleppo as people flee shelling. Intense clashes have been under way for more than a week between the regime and rebels in Aleppo, Syria's commercial and cultural center.
Parts of Syria's largest city saw the fiercest clashes yet in the country's 16-month crisis on Saturday, July 28. About 200,000 people have fled fighting in Aleppo and surrounding areas in the past two days, a U.N. official says.
Fighting leaves vehicles damaged Saturday in the southwestern city of Daraa.
Syrians carry the body of a man allegedly killed in the bombardment of Sukari, southwest of Aleppo, by Syrian regime forces on July 27.
Destruction appears widespread in Homs on Friday, July 27, in a handout photo from the Syrian opposition Shaam News Network.
A Syrian opposition fighter takes aim during clashes with forces loyal to President Bashar al-Assad in Aleppo on Wednesday, July 25.
Family and friends mourn over the body of Usame Mircan, who they say was killed by a Syrian government sniper in Aleppo on Wednesday.
Usame Mircan's mother grieves after he was killed during fighting in Aleppo.
The bodies of men killed during clashes between Syrian rebel fighters and goverment forces lie on the Aleppo street on Thursday, July 26.
Fighters from the Syrian opposition rest at a former primary school in Aleppo on Wednesday.
Residents take cover as fighters from the Syrian opposition clash with forces loyal to President Bashar al-Assad in Aleppo on Wednesday.
Syrian rebels guard a checkpoint in Aleppo on Wednesday.
A damaged portrait of President Bashar al-Assad sits among piles of debris at a checkpoint manned by Syrian rebels in Aleppo on Wednesday.
Syrian rebels drive through Selehattin near Aleppo during clashes with government forces on Monday, July 23.
A Syrian rebel runs through the streets of Selehattin during an attack on a municipal building. The rebel Free Syrian Army says it is attempting to "liberate" several districts of Aleppo.
Syrian rebels work to find snipers during clashes Monday between the opposition and government forces in Selehattin.
Syrian rebels make their way down a street Monday in Selehattin near Aleppo. If they gain control of Aleppo, it would mark a pivotal point in the Syrian crisis.
Syrian rebels take cover behind sandbags during fighting Monday at the entrance to the city of Selehattin.
On Sunday, July 22, a Syrian refugee looks out from a bus as he arrives at a refugee camp in Turkey opposite the Syrian commercial crossing point Bab al-Hawa.
Syrian refugees flee from a refugee camp nicknamed "Container City" on the Turkish-Syrian border in Kilis province, southern Turkey, on Sunday.
A mortar shell falls toward the Syrian village of Jbatha Al-khashab, about 45 kilometers (28 miles) south of Damascus. It's seen from the Israeli side of the border, in the Golan Heights.
Smoke from artillery shelling rises above Jbatha Al-khashab.
An armed Syrian rebel wearing the jersey of FC Barcelona rests with comrades near the northern city of Aleppo on Sunday. The rebel Free Syrian Army announced the start of the battle to "liberate" Aleppo, Syria's commercial hub and a traditional bastion of President Bashar al-Assad's regime.
A Free Syrian Army soldier rips a portrait of President Bashar al-Assad at the Bab Al-Salam border crossing to Turkey on Sunday.
Dozens of Turkish truck drivers on Saturday, July 21, accused Free Syrian Army rebels of having burned and looted their lorries as they captured Syria's Bab al-Hawa post, near Aleppo, from government troops.
In this photo released by the Shaam News Network, a truck burns after shelling in the Erbeen suburb of Damascus on Saturday, July 21.
Refugees fleeing the violence in Syria arrive by bus in Baghdad, Iraq, on Saturday.
Turkish soldiers stand guard at the Cilvegozu border gate in Reyhanly that connects to Syria's Bab al-Hawa post. An estimated 120,000 people have fled Syria to Turkey, Iraq, Lebanon and Jordan.
Burned-out trucks at the Bab al-Hawa Syrian border post with Turkey on Friday, July 20. Syrian rebels seized control of the post after a fierce battle with Syrian troops, an AFP photographer at the scene reported.
Syrian soldiers celebrate in the al-Midan area in Damascus on Friday. Syrian regime forces routed rebel fighters from the Damascus neighbourhood of Midan, Syrian state television reported, saying troops had "cleaned" the district of "terrorists."
Journalists are shown a dead body on a government tour of the al-Midan area in Damascus on Friday.
Members of Syria security forces rest in the al-Midan area in Damascus on Friday.
Syrian army soldiers hang their national flag in a partially destroyed neighborhood in the al-Midan area in Damascus.
Smoke hangs in the air in a partially destroyed neighborhood in the al-Midan area in Damascus.
Members of Syria security forces pose for photographers in the al-Midan area in Damascus after driving out the rebel fighters.
Syrian residents take goods from a truck that rebels captured at the Bab al-Hawa border crossing with Turkey on Friday.
A picture released by the official Syrian Arab News Agency on July 19 shows Syrian General Fahd al-Freij meeting with President Bashar al-Assad in Damascus after his swearing-in ceremony as defense minister.
A man holds up a picture of President Bashar al-Assad at a former police station in Atareb after clashes between Syrian soldiers and Free Syrain Army near Aleppo on Thursday, July 19. Rebels seized control of border crossings with Iraq on Thursday, dealing a new blow to al-Assad, as China and Russia dismayed the West by blocking U.N. action against his regime.
People walk along the street in Atareb amidst damage caused by clashed between Syrian soldiers and the Free Syrian Army.
A Syrian man checks the former police station of Syrian regime after a clash at Atareb on Thursday.
Smoke ascends from from alleged shelling of the Syrian village of Jebata al-Khashab as seen from the hill village of Buqaata in the Israeli-annexed Golan Heights on Thursday.
The death toll in Syria on July 12 reached 287, making it the bloodiest day in Syria since the uprising began. As it has done consistently, Syrian state television blamed "armed terrorist groups" for the killings.
A Syrian woman sits with her grandson outside a damaged building after attacks in the Syrian village of Treimsa on July 13, 2012. More than 200 people were massacred in the town, according to activists.
A Syrian demonstrator holds an opposition flag during a protest in Damascus on July 2, 2012. There have been increasing reports of violence in the Syrian capital.
Syria's President Bashar al-Assad waves as he arrives for a speech to Syria's parliament in Damascus on June 3, 2012. The embattled president denied that government forces were behind the "outrageous" massacre in Houla.
People gather at a mass burial on May 26, 2012 for victims reportedly killed during an artillery barrage from Syrian forces in Houla. The attack left at least 108 people dead, including nearly 50 children, according to the United Nations.
Members of the Free Syrian Army return to Qusayr on May 12, 2012 after an attack on Syrian regime forces in the village of Nizareer, near the Lebanese border in Homs.
A U.N. observer speaks with Syrian rebels and civilians in the village of Azzara on May 4, 2012, days before the country's parlianemtary polls were held against a backdrop of unrest.
Thousands of Syrians wave their national flag and hold portraits of President Bashar al-Assad and Lebanon's Hezbollah chief Hassan Nasrallah, right, during a rally to show support for their leader on March 29, 2012 in Damascus.
Syrian rebel fighters man a checkpoint leading into the town of Taftanaz in the rebel stronghold province of Idlib on March 20, 2012.
A Free Syrian Army rebel mounts his steed in the Al-Shatouria village near the Turkish border in northwestern Syria on March 16, 2012, a year after the uprising began. The Free Syrian Army is an armed opposition group made up largely of military defectors.
Syrian refugees walk across a field before crossing into Turkey on March 14, 2012. International mediator Kofi Annan called for an immediate halt to the killing of civilians in Syria as he arrived in Turkey for talks on the crisis.
A day after the twin suicide bombings, Syrian mourners pray over the coffins of the 44 people killed during a mass funeral in Damascus.
A Syrian man who was wounded in a suicide attack rests at a hospital in Damascus on December 23, 2011. Suicide bombers hit two security service bases in the Syrian capital, killing dozens of people.
Arab foreign ministers attend an emergency meeting at the Arab League headquarters in Cairo on October 16, 2011, to discuss the crisis in Syria.
U.S. Secretary of State Hillary Clinton speaks to the media in Washington on August 18, 2011. Clinton said U.S. sanctions on Syrian oil "strike at the heart of the Syrian regime."
Syrian youths wave national flags while army troops drive out of Daraa on May 5, 2011. During a week-long military lockdown of the town, dozens of people were reportedly killed in what activists described as "indiscriminate" shelling on the city.
Syrians in Damascus protest in the street on March 25, 2011, after clashes with government forces in Daraa left several dead.
Supporters of Syrian President Bashar al-Assad rally on April 1 in Istanbul, Turkey, as delegates from dozens of countries gather to push for ways to end the deadly violence in Syria. The United Nations estimates more than 10,000 people have been killed since the beginning of the crisis in March 2011. The conflict is now being labeled a civil war by the International Committee of the Red Cross.
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Photos: Showdown in Syria
"This is like punishment from the regime. They want to make people hungry," she said.
Protests against Syrian President Bashar al-Assad, whose family has ruled the country for more than 40 years, began in March 2011. Security forces launched a violent crackdown on peaceful protests that has been met by increasingly stiff resistance, with large numbers of government troops joining the opposition.
The conflict has now claimed nearly 17,000 lives, U.N. Secretary-General Ban Ki-moon said last week, while opposition activists put the toll at more than 20,000.
Video: The changing mission of U.N. in Syria
In Iran, one of Syria's few remaining allies, Foreign Minister Walid Moallem vowed Monday that the rebels would not take Aleppo.
"Since last week, (opposition fighters) planned for whatever they called the 'great Damascus battle,' but they have failed after one week," Moallem said, referring to a rebel offensive beaten back earlier this month. "That's why they moved to Aleppo, and I can assure you that they will fail."
Blog: A bloody mess could get messier
In Turkey, where more than 43,000 Syrians have taken refuge since the crisis began, two convoys of Turkish troops, including tanks, were seen moving into the border town of Kilis. A high-ranking police official from the Syrian city of Latakia defected to Turkey on Monday, as well as 11 other Syrian officers, the Turkish Foreign Ministry said.
In Paris, French Foreign Minister Laurent Fabius said his country will take more action to try to stop the bloodshed when it assumes the rotating presidency of the U.N. Security Council on Wednesday.
"We are going to ask -- before the end of the week -- for a meeting of the Security Council, probably at a ministerial level ... to try and stop the massacres and prepare for the political transition," Fabius told French RTL radio on Monday.
In London, the top diplomat at the Syrian Embassy resigned his post, the British Foreign & Commonwealth Office said. Charge d'Affaires Khaled al-Ayoubi told British officials that he was "no longer willing to represent a regime that has committed such violent and oppressive acts against its own people," the office said in a statement.
In Washington, the White House said President Barack Obama and Turkish Prime Minister Recep Tayyip Erdogan "shared their growing concerns about the Syrian regime's ruthless attacks against its own people, most recently in Aleppo, and the deteriorating humanitarian conditions throughout Syria as a result of the regime's atrocities" in a telephone call Monday.
"The two pledged to coordinate efforts to assist the growing numbers of displaced Syrians, not only within Syria, but in Turkey and the broader region. The president acknowledged the generosity of the Turkish people in hosting so many Syrians who have fled their homes in search of safety in Turkey."
Read more: After the fall of the House of Assad, could Syria be worse?
And in Tunisia, his first stop on a visit to the Middle East, U.S. Defense Secretary Leon Panetta told CNN that al-Assad "knows he's in trouble, and it's just matter of time before he has to go."
Asked what he'd say to the embattled Syrian leader, Panetta said, "I would say if you want to be able to protect yourself and your family, you better get the hell out now." Sunday, he predicted that the crackdown in Aleppo will prove "a nail in Assad's coffin" by turning even more people against the government.
The United States is providing nonlethal aid to the rebels, including communications gear. Other countries are providing more direct miltary aid, "So there is no question that one way or another, they are getting the support they need in order to continue this fight," Panetta said.
CNN's Barbara Starr and Yesim Comert contributed to this report.