Damascus: Rebels on Friday overran Taftanaz airbase in north Syria, a watchdog said, marking a significant advance that came as peace envoy Lakhdar Brahimi met with top US and Russian officials on the Syrian crisis.

“The fighting at Taftanaz military airport ended at 11am (0900 GMT) and the base is entirely in rebel hands,” said Syrian Observatory for Human Rights director Rami Abdul Rahman.

The base soon thereafter, however, came under aerial attack by government fighter jets, the Britain-based Observatory said in a later statement.

“Warplanes are bombing Taftanaz military airport in an attempt to destroy it,” it said.

The capture of the base marks an important advance for the rebels, who control vast swathes of Syria’s north and east and are battling President Bashar Al Assad’s forces in most major cities, including on the outskirts of Damascus.

“This is the largest airbase to be seized since the revolt began” nearly 22 months ago, Abdul Rahman said.

The rebels have previously taken control of the relatively small Hamdan airport in Albu Kamal on the Iraqi border in the east, and the Marj Al Sultan military airport in Damascus province.

The assault on Taftanaz was led by jihadist fighters from the Al Nusra Front, Ahrar Al Sham and Islamic Vanguard battalions, as well as other rebel groups, the Observatory said.

Many soldiers and officers fled the base at dawn, while the total number of casualties for each side was not immediately available.

The rebels seized several military vehicles and a major weapons depot.

Government forces, however, managed to pull out most of the 60 helicopters deployed at the airbase, leaving behind 20 choppers that are no longer in working condition, the Observatory said.

News of the capture of the airbase came as Brahimi, the UN-Arab League special envoy on Syria was meeting in Geneva with Russian Deputy Foreign Minister Mikhail Bogdanov and US Undersecretary of State William Burns.

They made no comment as they arrived for the closed-door talks at the UN headquarters in Geneva.

The discussions are taking place a day after Syria accused Brahimi of “flagrant bias”, casting doubt on whether he could stay on as international mediator.

Damascus lashed out at the veteran Algerian diplomat after he described proposals Al Assad made on Sunday for a “political solution” to the 22-month conflict as “one-sided”.

Brahimi attacked Al Assad’s plan to keep fighting rebel “terrorists” and ignore opposition groups tied to them, in comments to the BBC.

He also questioned the decades-long rule by Al Assad’s family, saying that in Syria, where Al Assad took over from his long-ruling father in 2000, “what people are saying is that one family ruling for 40 years is a little bit too long.”

Syria’s pro-government Al Watan newspaper denounced Brahimi as a “pawn” of the West, and Syria’s foreign ministry accused him of “flagrant bias for those parties known to be conspiring against Syria and its people”.

Opposition activists meanwhile called for Friday demonstrations to denounce the “death camps”, an allusion to the suffering of Syrian refugees living in tent settlements in neighbouring countries, which this week were hit by snowstorms and floods.

The call for protests comes as the UN said that 612,134 Syrians had been registered as refugees in the region or were in the process of being registered, a sharp rise from the 509,550 announced on December 11.

In a related development, oil-rich Saudi Arabia announced on Friday it was sending aid to the value of $10 million (Dh36.7 million) to Syrian refugees in Jordan affected by the worst winter storms to lash the region in the past decade.