Rebel are reported to have taken control of a strategic military airbase in north-western Syria after weeks of fierce fighting with government forces.
Online videos appeared to show rebels celebrating inside Taftanaz airport, alongside tanks and helicopters.
Helicopters based there have been used to attack rebel-held areas.
Meanwhile, talks in Geneva between the UN envoy to Syria, Lakhdar Brahimi, and senior US and Russian diplomats ended without a breakthrough.
Mr Brahimi had wanted to discuss with the US Deputy Secretary of State, William Burns, and Russia's Deputy Foreign Minister, Mikhail Bogdanov, how to implement the plan proposed by the Action Group for Syria in June, which called for an immediate cessation of violence and the establishment of a transitional government.
A joint statement read by Mr Brahimi after Friday's meeting stated that all sides had stressed there could be no military solution to the conflict, and underscored the necessity to reach a political solution.
Responding to a question, he said: "If you are asking whether there is a solution around the corner, I'm not sure that is the case."
On Sunday, Syrian President Bashar al-Assad made a defiant speech with no sign he would step down, something Washington has demanded. However, Moscow says Syrians alone should decide their future.
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. One video purportedly showed helicopters at Taftanaz, some of which appeared to be intact.
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.
There was no immediate word on casualties among rebel or government forces, although the bodies of 10 soldiers could be seen in videos.
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 69 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.
The UN recently said more than 60,000 people had been killed since the uprising against the president began in March 2011.