BEIRUT (AP) — A Syrian activist group says scores of rebels are attacking a sprawling air base in the northern province of Idlib.

The Britain-based Syrian Observatory for Human Rights says the assault on the Taftanaz base began early Wednesday.

Observatory director Rami Abdul-Rahman described the attack as one “of the most intense” on the airfield.

In the past few weeks, Syrian rebels have stepped up their attacks on airports around the neighboring Aleppo province, trying to chip away at the government’s air power, which poses the biggest obstacle to the opposition fighters’ advances.

Rebels have attacked the Taftanaz base in the past but have failed to capture the facility.