A car bomb ripped through a residential area of Syria's second city Aleppo on Sunday, a day after twin blasts killed 27 in the capital Damascus.  

State news agency SANA said the attack by "terrorists" had killed two people and wounded 30 others. Opposition activists said three died in the explosion, close to a Political Security office and a church.

The semi-official news channel al-Ikhbariya said security forces had been tipped off about the bomb and had been moving residents out of the area when it went off. It said the car had been filled with 200 kilograms of explosives.

Pictures on the SANA website showed building fronts blasted open and aid workers standing near piles of shattered masonry and bomb craters. Syria TV showed at least one street corner splattered in blood.

Local activist Mohammed Halabi said at least 15 ambulances and security cars rushed to the area after the blast.

"The blast was extremely loud and even shook nearby areas," Halabi said, speaking by telephone from Aleppo.

No group claimed responsibility for the attack, and an activist in Aleppo from the opposition's local Revolutionary Council said the government was behind the explosion.

"They want to make our uprising seem like a terrorist operation to the rest of the world, but it is not," said the activist called Marwan, who spoke to Reuters by telephone.

Clashes, raids across Syria

Opposition groups reported heavy raids by security forces and fighting with rebels in northern and southern Syrian provinces as well as suburbs of Damascus.

A sniper shot dead a man in southern Deraa, according to the Syrian Observatory for Human Rights, and security forces killed three people during raids in a village in northern Idlib, including a 14-year-old boy.

In the capital, as crowds gathered for memorials to victims of Saturday's car bombs, activists said security forces beat and arrested people at a march of more than 200 when protesters began shouting "the people want to topple the regime".

The phrase has echoed through the wave of Arab uprisings that began last year and has toppled autocratic rulers in Tunisia, Egypt, Libya and Yemen.

"They were walking through an area in central Damascus, near SANA (the state news agency). At first they shouted slogans against violence and the police didn't do anything, but as soon as they started to call for regime change the police rushed in and started beating people with canes," said Rami Abdelrahman, from the British-based Observatory.

The protest, which called for non-violent resistance to the government, had been led by moderate opposition leaders previously tolerated by the government because of their calls for dialogue and rejection of foreign intervention.

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

Security forces beat and arrested Mohammed Sayyed Rassas, a leader of the National Coordinating Body for Democratic Change (NCB), an opposition group which had visited China and Russia in attempts 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, arguing the government's fierce crackdown has made arming the uprising inevitable.

Syrian government forces have crushed a rebel stronghold in the central city of Homs and have been pounding rebel strongholds in northern Idlib.

"It's clear that the battle is finishing in the regime's favor overall," said a Lebanese official close to Assad's government.

"On the security level there is a long and difficult struggle for the regime and it is obvious this will take a long time to finish ... We will see many more explosions like those we saw on Sunday but in general they have finished off the military fight and they don't have much more to do."

Thousands took to the streets in an anti-government protest in Deraa after the sniper's killing of a resident on Sunday, according to the Observatory, which has a network of activists in Syria.

Reports from Syria are difficult to verify as the government has restricted access to foreign journalists.

Damascus memorial

In Damascus, crowds of mourners carried the coffins of the 27 bomb victims, draped in Syrian flags and covered in bouquets of flowers.

The head of the Arab League, Nabil Elaraby, condemned the twin bombings and called  in a statement for "an immediate halt of all acts of violence regardless of the source and for an active move to find ways of stopping gunfire in all parts of Syria ... to reach a way to guarantee Syria's transition into a peaceful stage dominated by dialogue."

The United Nations says more than 8,000 people have been killed by security forces in the crackdown on a revolt against four decades of rule by the Assad family.

The struggle has become increasingly bloody as peaceful protest has given way to rebellion by armed groups. Authorities say they are fighting foreign militants who have killed more than 2,000 members of the security forces.

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

In southern Deraa, birthplace of the uprising, Syria TV showed video of a bridge blown up by rebels. It had been used to transport supplies to security forces who surround the city.

The Observatory said security forces raided the town of Artouz, a Damascus suburb, looking for wanted men. Other activists said they could hear heavy gunfire in the area.

At the site of the Damascus blasts, Syria TV showed dozens of people waving Syrian flags gathered to pray for the victims.

"Whatever they want to do we won't be afraid," said one woman speaking to the channel. "We are with President Assad ... those who don't love Damascus should leave."