Activists say rebels have attacked an air base in northern Syria but failed to capture it.

The Britain-based Syrian Observatory for Human Rights says the fighting concentrated near the command center in Mannagh air base, under rebel siege for months. It said rebels fired tank shells at the building.

The attack on Mannagh came after Syrian troops backed by Lebanese Hezbollah fighters captured the strategic central town of Qusair near the border with Lebanon on Wednesday.

Aleppo-based activist Mohammed Said said rebels failed to advance in the attack on the air base that continued until early Friday.

Syria's conflict started with largely peaceful protests against President Bashar Assad's regime in March 2011 but turned into a civil war.

More than 70,000 people have been killed, according to the United Nations.