Rebels battle into the night to control a helicopter base just outside Damascus.

They say they destroyed two helicopters and took 15 people captive.

It is their latest gain in a costly battle to unseat President Bashar al-Assad.

The video, which could not be independently verified by Reuters, comes as rebel forces draw nearer to Assad's seat of power.

A Western diplomat told Reuters that Assad still had the upper hand in the fight.

It's a fight that activists say has already cost the lives of 40,000 people.