At least seven people were killed when a blast ripped through a bus carrying Shiite pilgrims in a central district of the Syrian capital on Sunday, a monitoring group said.
The Syrian Observatory for Human Rights said it was not immediately clear what had caused the blast near the Souq al-Hamadiyeh neighbourhood of Damascus.
The explosion was also reported by Syrian state media, with the official SANA news agency saying at least four people had been killed and 19 wounded.
Observatory director Rami Abdel Rahman said the bus had a Lebanese licence plate and was carrying Shiite Muslim pilgrims visiting religious sites in the city.
Lebanese media reported that Lebanese nationals were among the dead and wounded, but there was no immediate official confirmation.
Syrian state television showed footage from the scene of the blast, with men in military uniforms picking through the wreckage of the bus.
Its front half was mostly blown off, leaving only the metal frame, and bags of belongings were strewn across the remaining seats.
The channel also showed images from inside a hospital where the wounded were being treated, including a woman whose black robes had been lifted up, revealing a bloodsoaked undershirt.
Parts of Damascus have remained relatively unscathed by the fighting raging across much of Syria since an uprising erupted in March 2011.
But rebels regularly fire rockets into the capital from rear bases in the surrounding countryside, and the city has also been hit by bombings.
Despite the conflict, the road from the Lebanese border to Damascus remains relatively safe, and Lebanese Shiite pilgrims have continued to visit religious sites in Syria.
More than 200,000 people have been killed in Syria since the conflict started, and around half of the country's population has been displaced.
Source: AFP