Clashes erupt near airport in Damascus

Syrian warplanes and artillery have hit targets near Damascus International Airport, following a bloody day of attacks in the Syrian capital that killed dozens and struck deep into President Bashar Assad's seat of power.

There were no immediate reports of casualties from today's shelling, which targeted the towns of Beit Sahm and Shebaa near the main airport road south of the capital.

Clashes in rebel strongholds of Daraya and Moadamiyeh, south-west of Damascus, were reported by the Britain-based Syrian Observatory for Human Rights and the Local Co-ordination Committees.

Recent rebel advances in the Damascus suburbs, combined with the bombings and three straight days of mortar attacks, mark the most sustained challenge of the civil war for control of Mr Assad's powerbase.

Syrian state media said the car bombing yesterday in the heart of Damascus - near the ruling Baath Party headquarters and the Russian Embassy - was a suicide attack that killed 53 civilians and wounded more than 200, including children. Anti-regime activists put the death toll at 61, which would make it the deadliest Damascus bombing of the revolt.

The main opposition group, the Syrian National Coalition, condemned the attack without accusing any specific group of carrying it out. It did, however, suggest that the regime allowed foreign terror groups to operate in Syria.

"The terrorist Assad regime bears the most responsibility for all the crimes that happen in the homeland because it has opened the doors to those with different agendas to enter Syria and harm its stability so it can hide behind this and use it as an excuse to justify its crimes," the group said in a statement.

There was no immediate claim of responsibility for the attack, but suspicion is likely to fall on one of the most extreme of Syria's myriad rebel factions, the al Qaida-linked Jabhat al-Nusra. The group, which the US has designated as a terrorist organisation, has claimed similar past bombings against regime targets.

Today, the Coalition said it would welcome US and Russian mediation to negotiate a peace deal to end the country's civil wall but insisted it would not allow Mr Assad or members of his security services to participate in the talks.

The announcement came in a statement posted on the Coalition's Facebook page following two-day meetings in Cairo meant to try to firm up its position on whether to engage with the regime in talks.

"Bashar Assad and the security and military leadership responsible for the state of Syria today must step down and be considered outside this political process," the statement said. "They cannot be part of any political solution for Syria and must be held accountable for their crimes."

The violence in Damascus follows a string of tactical victories in recent weeks for the rebels - the capture of the nation's largest hydroelectric dam and the overtaking of air bases in the north-east - that have contributed to the sense that the opposition may be gaining momentum.

But Damascus is the ultimate prize in the civil war, and many view the battle for the ancient city as the most probable endgame of a conflict, which has killed nearly 70,000 people, according to UN estimates.

AP