Video published by activists recorded heavy gunfire and explosions. A trail of fresh blood on a sidewalk in the suburb of Qudsiya led into a building where one casualty was taken. A naked man writhed in pain, his body pierced by shrapnel.

The Syrian state news agency SANA said "armed terrorist groups" had blocked the old road from Damascus to Beirut.

"The clashes led to the killing of tens of terrorists, wounding a large number of them, arresting others and seizing their weapons which included RPG launchers, sniper rifles, machineguns and a huge amount of ammunition," the agency said.

Syrian state television said rebels had kidnapped four-star airforce general Faraj Shahadeh from his home in the heart of Damascus on Tuesday, and that a special forces unit was trying to rescue him. It gave no further details.

The Syrian Observatory for Human Rights reported heavy fighting near the Republican Guard headquarters in Qudsiya, and in the Damascus suburbs of al-Hama and Mashrou' Dumar, just 9 km (6 miles) outside the capital.

It said 38 civilians and 24 troops had been killed during the day across Syria.

Samir al-Shami, an activist in Damascus, said tanks and armoured vehicles were out on the streets of the suburbs and some activists reported that one tank had been blown up.

The British-based Observatory, which has a network of activists across Syria, said security forces and armoured vehicles stormed the neighbourhood of Barzeh, an opposition toehold inside Damascus, and there were sounds of heavy gunfire.