Syrian opposition fighters have overrun Taftanaz airbase, the largest in northern Syria, after several days of fierce combat, the Syrian Observatory for Human Rights has said.

Anti-government activists said fighters from Jabhat al-Nusra and other groups opposed to President Bashar al-Assad seized control of buildings, ammunition and military equipment in the sprawling Taftanaz airbase in northern Idlib province on Friday.

"The fighting at Taftanaz military airport ended at 11:00 am (09:00 GMT) and the base is entirely in rebel hands," said Rami Abdel Rahman, the director of the UK-based rights group, on Friday.

"Many regime forces have been killed and most of the soldiers and officers fled at dawn," he told the AFP news agency by phone.