BEIRUT: 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, activists said.    

The Taftanaz air base in the northern Idlib province is considered the biggest field in the country's north for helicopters used to bomb rebel-held areas and deliver supplies to government troops.

Rebels from the Al Qaeda affiliated Jabhat al-Nusra and other Islamic groups have been fighting for weeks for control of the sprawling 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.

Rami Abdul-Rahman, director of the Britain-based Syrian Observatory for Human Rights (SOHR) said it is the first major military airport to fall into rebel hands.

He said warplanes bombed it after the rebel takeover, but the report could not be immediately confirmed.

The 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.

The aircraft were likely moved to the nearby Mastuma camp and the neighbouring town of Fuaa, according to the watchdog.

The rebel assault was part of a wider campaign to chip away at the Syrian government's air supremacy, which it has relied upon increasingly over the past year as it lost control of large swaths of territory. Airstrikes by warplanes and helicopters have proved the main obstacle to opposition fighters.

The rebels have been besieging Taftanaz for months, launching a fresh offensive on it in early November. While its fall will embarrass the regime, it will do little to stop airstrikes by government jets, many of which come from bases farther south.

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.

Activists estimate that around 700 rebels are involved in the offensive on Taftanaz, almost all of them Islamic militants. They include members of Jabhat al-Nusra, affiliated with Al Qaeda, and groups with a similar Islamic ideology.

Members of al-Nusra, which the US has branded a terrorist organisation, have been among the most effective fighters in the rebels' battle to oust Assad.

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