Syrian state media say an enormous blast Tuesday in the Marjeh district of the capital killed at least 13 people and wounded 70 others.
It was the second day in a row that an explosion has ripped through Damascus, sending plumes of thick black smoke into the air.
The intended target is not clear and no one has claimed responsibility but the explosion took place near the old Interior Ministry building. The nearby 28-story Damascus Tower office building was also damaged, along with several vehicles.
The state-run SANA news agency blamed the explosion on terrorists, a term Syrian officials frequently use to describe those fighting to oust President Bashar al-Assad. Witnesses also reported gunfire in the area after the bombing.
The explosion Tuesday comes a day after Syrian Prime Minister Wael al-Halqi escaped a bomb attack against his convoy on the west side of Damascus. The observatory said that blast killed six people, including five civilians.
Opposition forces have been increasing their attacks on Damascus as the fighting has dragged into its third year. The United Nations says more than 70,000 people have been killed in the violence.