Insurgents battled with troops on the perimeter of the Aleppo international airport, besieging the nearby military Brigade 80 in an attempt to push through to the airport itself, the Syrian Observatory for Human Rights said.

At the same time, hundreds of fighters with two hardcore Islamist rebel groups, the Al-Nusra Front and Ahrar al-Sham, fought soldiers around the Taftanaz airbase in the northwest province of Idlib, the British-based Observatory said.

The rebels had broken into the airport the day before after launching a car bomb at the main gate but were pushed back by the army.

The Aleppo facility is an important strategic prize in Syria’s north, which is largely under rebel control.