A car bomb hit Syria's second city Aleppo on Sunday, a day after blasts killed 27 in Damascus, and security forces arrested and beat activists at a rare anti-government protest in the capital.
Residents told the British-based Syrian Observatory for Human Rights they saw bodies in the streets of Aleppo.
The organization said initial reports suggested three people had been killed and about 25 injured in the blast.
The opposition 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 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".
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 Syrian Observatory for Human Rights.
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.
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.
