A bomb exploded in central Damascus near the hotel used by the UN observer mission in Syria on Wednesday, wounding three people, Syrian state television reported.
It said the blast, in the Abu Remanih area near a military depot and the trade union headquarters, was caused by a bomb planted on a fuel truck.
Several ambulances rushed to the scene and a security cordon was set up, according to witnesses.
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Activists said massive explosions echoed across much of the city and a video released by one opposition group showed a vast plume of smoke billowing into the sky.
The United Nations mission was not immediately available for comment.
Damascus has been rocked by several bomb blasts, including an attack last month at the national security headquarters that killed three of President Bashar al-Assad's top security chiefs.
The head of the UN Supervision Mission in Syria (UNSMIS), General Babacar Gaye, had staged a press conference the hotel, the Dama Rose, on Monday.
The UN Security Council is due to meet on Thursday to discuss the future of the observer mission, whose mandate expires on August 19.
