BEIRUT — Syrian rebels and Islamic militants seeking to topple President Bashar Assad took full control of a strategic northwestern air base Friday in a significant blow to government forces, seizing helicopters, tanks and multiple rocket launchers, activists said.


The Taftanaz air base in Idlib province is the largest air base yet to be captured by the rebels –and it is the biggest field in the north of the country for the helicopters that the regime has used to bomb rebel-held areas and deliver supplies to government troops.


The capture further chips away at the regime’s airpower in the north, which the regime has relied upon increasingly over the past year as it lost control of large swaths of territory. But it doesn’t eliminate the threat to rebels from the air. There remain several other, smaller helicopter bases, and regime warplanes that also strike the area operate from bases further south. The capture wouldn’t affect the military’s airpower against rebels in other parts of the country.


But the fall of the base is a new embarrassment for the regime, a sign of its fraying hold in the north. It also provides a strong boost for the arsenal of the rebels, who partially rely on weapons looted from the military.


Rebels from al-Qaida affiliated Jabhat al-Nusra and several other, mainly Islamist brigades have been fighting for weeks for control of the sprawling Taftanaz facility and broke into it on Wednesday evening. Activists said the rebels seized control of buildings, ammunition and military equipment after ferocious fighting at dawn.


“As of now, the rebels are in full control of the air base,” said Idlib-based activist Mohammad Kanaan. He acknowledged that government airstrikes will not stop, but said the base’s fall puts “another big nail in the coffin of the regime.”


A video taken by activists inside the base and posted online showed helicopters in the field, some of which appeared intact while others were destroyed.


“These are the helicopters that belonged to Assad’s regime and now they are the helicopters of the Syrian people,” said the narrator as he reached a parked helicopter that looked intact.


The video showed rebels dismantling ammunition from a heavy machine gun in the base and loading the ammunition into a truck. In other videos, rebels are seen celebrating inside the base, some kneeling and kissing the ground and others showing off booty including multiple rocket launchers.


The videos appeared genuine and corresponded to other AP reporting on the events depicted.


The weaponry at the bases is a key prize for the rebels, though it is not clear whether they can use the helicopters themselves. Rebels have captured helicopters in the past but there’s been no reported case of them flying one.


Kanaan, the activist in Idlib, said the rebels seized tanks and helicopters at the base, but added that most if not all of the helicopters were damaged from the fighting and were nonfunctional. The Syrian Observatory for Human Rights, an anti-Assad activist group, said around 20 helicopters were seized but none were in working order.


In one video, at least six dead men in military uniform were seen on the ground outside one of the housing units in the base. Two other dead men were seen inside the building. “They refused to defect. We have been urging them to defect since our attack began 10 days ago,” the rebel narrating the video said.


Another video released by the Observatory showed at least four dead men in uniform, including two who were wearing pilots’ costumes, in what appeared to be a trench.


There was no immediate word on casualties among rebels.


The rebels had been attacking Taftanaz for months, launching a fresh offensive on it in early November with a force activists estimated at about 700 fighters, almost all of them Islamic militants.


The assault was also a sign of the strength of Islamic hardliners within the rebel ranks. The fighters included members of Jabhat al-Nusra, a group affiliated with al-Qaida that includes many foreign jihadis, along with Syrian rebel groups with a similar ideology. Frighters from al-Nusra, which the U.S. has branded a terrorist organization, have been among the most effective in the rebels’ battle to oust Assad.


Last week, the rebels began major attacks on three other air bases in Idlib and the nearby province of Aleppo.


Taftanaz lies near the highway between the capital Damascus and the northern city of Aleppo, a major front in the civil war that has stood at a stalemate for months.


But it is unclear if the rebels will try to retain control of Taftanaz. The Britain-based Observatory, which relies on a network of activists on the ground, said government warplanes bombed the air base after the rebel takeover Friday.


The opposition has seized several other air defense bases in the north and Damascus suburbs, making off with weapons and ammunition, but in most cases has not managed to retain the facilities.


Until the fall of Taftanaz, the biggest capture had been that of the Marj al-Sultan base just outside the capital Damascus. The base was mostly used for fixing helicopters but the rebels captured several choppers in it.