Rebels attacked a sprawling air base in northern Syria on Wednesday as the opposition expanded its offensive on military airports in an attempt to sideline a major weapon in the hands of President Bashar Assad's forces.

The Britain-based Syrian Observatory for Human Rights said the rebel assault on the Taftanaz base was preceded by heavy shelling of the area, and the fighters appeared to be trying to storm the facility. Observatory director Rami Abdul-Rahman described the attack as one "of the most intense" on the airfield.