State media in Syrian say as many as 25 people have been killed in a suicide bomber on a district in central Damascus.
State news agency Sana said 46 had been injured.
State TV has shown pictures of blood-spattered streets in the capital after the explosion, which was blamed on terrorists.
Most of those killed were civilians, but some security personnel were reported to be among the casualties.
Forty four people died in similar blasts two weeks ago which were also blamed on terrorists. The opposition accused the government of staging them.
Syrian Revolution General Commission (SRGC), inside Syria, told the BBC it had nothing to do with the latest explosion.
A spokesman said he feared there would be more.
