Syrian jets bombed rebel-held areas of Damascus today, residents said, and a countrywide internet blackout entered its third day.

Syrian rebels fighting to oust President Bashar al-Assad clashed with troops in most populated areas of the country, according to opposition activists.

At least 40,000 people have been killed during the 20-month-old uprising, they say.

The Syrian Observatory for Human Rights, an opposition-linked monitor, said war planes were bombing the Damascus suburbs of Kafar Souseh and Darraya.

If rebels maintain a presence in these areas, they will hold ground in a continuous arc from the northeast to southwest of the capital's outer districts.

"Syrian regular forces are trying to control the areas surrounding the capital and clashed with rebel fighters," the Observatory said.

The mostly Sunni Muslim rebels battling Mr Assad, who is from Syria's Alawite minority linked to Shia Islam, have been making gains across Syria by overrunning military bases and have been increasing attacks on Damascus, his seat of power.

Since Thursday, clashes have been reported near the Aqraba and Babilla districts on the southeastern outskirts of Damascus which lead to the international airport, effectively closing the road and leading EgyptAir and Emirates to suspend flights.

Syrian state television quoted a ministry of information statement saying the Damascus international airport was open today and that the road leading to it was safe.

Opposition activists said clashes continued.

Networking experts accuse the government of cutting off the internet but Damascus blames "terrorists," a term it uses for the opposition.

Rights groups have warned the communications drop off is a precursor to a wider offensive by government forces in the capital.

Syrian security sources and diplomats say the government intends to block central Damascus from the restive suburbs.

Rebels and activists said today there have been multiple communications problems since the uprising began.