An explosion rocked the central Maidan district of Damascus on Friday, killing 25 and wounding 46 people, Syrian state television said.
The television reported a "terrorist explosion" in Maidan but did not say what it had targeted.
"There is more security in Maidan than usual because it is Friday and there are lots of military and security checkpoints. We do not know what was targeted yet," said the resident, a private sector employee who declined to be named.
Another resident said: "I didn't hear anything, but a lot of streets are closed and everyone is really nervous."
Some opposition activists said the blast had targeted a police station, others said it was an intelligence building.
At least 44 people were killed last month by what the Syrian authorities said were two suicide bombings against security buildings in the Syrian capital.
Syria has been racked for 10 months by an uprising against President Bashar al-Assad in which the United Nations says more than 5,000 people have been killed. The government says armed "terrorists" have killed 2,000 members of the security forces.