A car bomb killed five people and wounded dozens in the eastern Damascus district of Qaboun on Saturday, the Syrian Observatory for Human Rights said.
Another activist group in Damascus gave no figures for the number of people killed in the blast but said bodies were still being recovered from wreckage caused by the explosion.
The British-based Observatory, which monitors violence across Syria through a network of sources on the ground, also reported clashes between rebel fighters and forces loyal to Syrian President Bashar al-Assad on the edge of the southern Damascus neighbourhood of Hajar al-Aswad.
The district is next to the Palestinian refugee camp of Yarmouk, which was taken over by rebels this week.
The Observatory says 44,000 people have been killed in Syria since the uprising erupted against Assad in March last year.