Heavy fighting breaks out in Damascus

The sound of heavy machineguns and rocket-propelled grenades echoed throughout the night from the western neighbourhood of al-Mezzeh.

The neighbourhood hosts several security facilities and is one of the most heavily guarded areas in Damascus. There were no immediate reports of casualties but residents said by telephone the fighting was intense. 

Al-Mezze has previously been the scene of large anti-government protests.

The latest fighting came a day after a car bomb in Syria's second biggest city of Aleppo killed at least three people, according to the Syrian Observatory for Human Rights.

Residents told the UK-based rights group that they saw bodies in the streets after Sunday's blast close to a state security office.

State news channel Syria TV said that Sunday's "terrorist" explosion took place between two residential buildings in the al-Suleimaniya district, behind a post office.

The opposition also reported heavy raids by security forces and fighting with rebels in northern and southern Syrian provinces and suburbs of Damascus.

In the capital, as crowds gathered for memorials to the 27 victims of Saturday's car bombs, security forces broke up an opposition march of more than 200 people when protesters began shouting "the people want to topple the regime".

Among those arrested and beaten was Mohammed Sayyed Rassas, a leader of the National Co-ordinating Body for Democratic Change (NCB), an opposition group which had visited China and Russia in attempt to promote dialogue between Assad and the opposition.

Most opposition groups have rejected the NCB over its insistence on non-violence and its stance against foreign intervention.

Security forces also arrested Farzand Omar, a doctor and politician from the party "Building the Syria State," when he arrived at the Damascus airport from his hometown of Aleppo.

State television blamed "terrorists" for the Saturday morning explosions and reported that vehicles packed with explosives had been used.

The blasts targeted buildings belonging to a customs office and air force intelligence. Most of the casualties were civilians, state television said. 

The channel broadcast interviews with Syrians who blamed the attack on the United States and Gulf nations, including Saudi Arabia and Qatar, who they said had sent "terrorists".

Bassma Kodmani, a Paris-based member of the opposition Syrian National Council, said she doubted the armed groups trying to bring Assad down by force have the capacity to carry out such attacks on security institutions in the capital.

"I don't think any of the opposition forces or the Free Syrian Army has the capacity to do such an operation to target these buildings because they are fortresses," she said.

"They are very well guarded. There is no way anyone can penetrate them without having strong support and complicity from inside the security apparatus."

SANA said a third blast went off near a military bus at the Palestinian refugee camp Yarmouk in Damascus later in the day, killing the two suicide bombers.

Activists said the Sunday march in Damascus aimed to commemorate the peaceful roots of Syria's uprising, which has been overshadowed by the growing armed insurgency against state security forces.

Heavy fighting also raged in the northwestern province of Deir Ezzor and military vehicles were torched, activists said.

Rebels also blew up a bridge in southern Deraa, birthplace of the uprising, the UK-based rights group said. The bridge had been used to transport supplies to security forces besieging the city.

The United Nations estimates that more than 8,000 people have died so far in the violence following the revolt against four decades of rule by the Assad family.

Syrian authorities say they are fighting insurgents who have so far killed more than 2,000 members of the security forces.