Syrian rebels seized a "large part" of a military airport near the capital on Sunday as troops shelled the outskirts of Damascus province, a watchdog and activists said.

The Syrian Observatory for Human Rights said that 31 rebels and 16 soldiers in and around Damascus were among 94 people killed in violence across the country on Saturday.

Rebels took a "large part" of the military airport of Marj al-Sultan, 15 kilometres (nine miles) east of Damascus, and destroyed two helicopters, according to the Britain-based Observatory.

A video posted on the Internet by activists appeared to show one wrecked helicopter, while a rebel shoots rockets at the airport, gripped by several fires.

The Syrian Revolution General Commission and Local Coordination Committees, two major networks of activists on the ground, meanwhile, reported shelling of several areas near Damascus.

Rebel fighters point to the sky as a Syrian army helicopter flies overhead in the town of Maarat al-Numa. Syrian rebels seized a "large part" of a military airport near the capital on Sunday as troops shelled the outskirts of Damascus province, a watchdog and activists said.

Helicopter gunships pounded Zamalka town, northeast of Damascus, as rebels clashed with troops in nearby Harasta, said the Observatory, which relies on a network of activists, lawyers and medics in civilian and military hospitals.

The opposition fighters have set up rear bases in orchards surrounding the capital, where they had made advances during the summer but have since been driven out.

In the southern province of Daraa, insurgents temporarily took control of a military outpost on the border with Jordan overnight, the Observatory said.

In the north, rebels pressed on with an offensive against troops stationed at the strategic Tishrin dam, which straddles the Euphrates river and connects the provinces of Aleppo and Raqa.

The rebels, according to a local resident, have been closing in on the area for the past week.

Opposition fighters already control one of the main routes to Raqa and the dam would give them a second passage, connecting a wide expanse of territory between the two provinces, both of which border Turkey.