Syrian rebels launched a major assault in the northwest on Saturday against the Taftanaz airbase used to launch strikes against their positions, activists and a watchdog said.
The Syrian Revolution General Commission, a network of activists on the ground, said an operation had begun "to liberate the Taftanaz airbase".
The Syrian Observatory for Human Rights, a Britain-based watchdog, said "heavy fighting" had broken out near the base, in Idlib province where rebels have made significant gains in recent days.
The rebels had earlier on Saturday seized an air defence position at Duwila in Idlib, in fighting that killed an army officer and wounded eight rebel fighters, the Observatory said.
After seizing arms and ammunition from the post, the rebels fled under attack from the air.
The rebels' offensive against air force positions came after the regime stepped up air strikes in recent days in a bid to reverse their gains.
The Observatory said rebels had also killed 21 soldiers and taken three positions in the town of Douma, northeast of Damascus, on Friday.
The positions comprised a police station, a municipal government building and a hospital, it said.
Nationwide, 181 people were killed in violence on Friday, according to the Observatory, which relies on a network of activists and medics in civilian and military hospitals for its figures.
It says more than 36,000 people have been killed since the uprising against President Bashar al-Assad's rule broke out in March 2011 as a protest movement inspired by the Arab Spring before escalating into an armed rebellion.