One video purportedly showed rebels driving armoured vehicles at TaftanazRebels are reported to have taken control of a strategic military airbase in north-western Syria after days of fierce fighting with government forces.
Opposition activists said the Free Syrian Army (FSA) was in full control of Taftanaz airport. Videos purportedly showed fighters inside the facility.
Helicopters based there have been used to attack rebel-held areas.
Meanwhile, top US and Russian officials are attending talks in Geneva with the UN envoy to Syria, Lakhdar Brahimi.
They were expected to discuss how to advance a peace plan proposed by world powers in June, but the BBC’s Imogen Foulkes says a diplomatic breakthrough is unlikely.
Ammunition store
Hundreds of FSA fighters – led by the jihadist groups al-Nusra Front, Ahrar al-Sham and the Islamic Vanguard – have besieged Taftanaz Military Airport in Idlib province since early November.
Helicopters based at the sprawling facility, which lies near the motorway between the capital Damascus and the second city of Aleppo, have been used to bomb rebel-held areas in the north and deliver vital supplies to government forces struggling to halt rebel advances.
Rebel fighters broke into the airbase on Wednesday night after days of fighting, and by Thursday had seized control of more than half of it.
On Friday morning, the Local Co-ordination Committees (LCC), an opposition activist network, reported that the FSA was now in full control.
Videos posted online purportedly showed Islamist fighters inspecting armoured vehicles outside the airbase’s main gate, and at an ammunition store inside the facility.
The Syrian Observatory for Human Rights (SOHR), a UK-based activist group, said the fighting had ended at about 11:00 (09:00 GMT).
“Many regime forces have been killed and most of the soldiers and officers fled at dawn,” Rami Abdul Rahman told the AFP news agency. “This is the largest airbase to be seized since the revolt began.”
The military had removed all its helicopters, except for 20 which were no longer in working condition, he added.
Mr Abdul Rahman said the military had struck back after the rebels captured the base, launching air strikes on their positions. The LCC also reported that a warplane had bombed the nearby town of Taftanaz.
On Wednesday, one opposition activist said the military had blown up aircraft at the base pre-emptively to prevent the rebels gaining access to them. The SOHR said 15 helicopters appeared to have been damaged.
The official Sana news agency said guards had “repelled a terrorist group that tried to storm the airport on Thursday”, inflicting heavy losses.
The LCC said more than 53 people had so far been killed across the country on Friday, including 40 people in Nahat al-Houl in the north-western province of Hassakeh. Government warplanes had carried out air strikes on the town overnight, it added.
Defiant
The violence came as the UN and Arab League envoy to Syria began further talks about a political solution in Geneva with the US Assistant Secretary of State, William Burns, and Russia’s Deputy Foreign Minister, Mikhail Bogdanov.
Officials said they would discuss how to implement the plan proposed by the Action Group for Syria in June, which called for an immediate ceasefire and the establishment of a transitional government that could include officials serving under Mr Assad and members of the opposition.
However, our correspondent says the mood ahead of the talks is not optimistic.
On Sunday, President Assad made a defiant speech with no sign he would step down, something Washington has been demanding for some time. Moscow however disagrees with such calls, saying Syrians alone should decide their future.
The UN recently said more than 60,000 people had been killed since the uprising against the president began in March 2011.