Witnesses in Syria's capital say a blast hit a bus that had been carrying Iranian Shi'ite pilgrims. Three people were killed and dozens of others wounded. The explosion coincided with a visit to Damascus by a top Iranian official.
The suburban Damascus blast took place near a major Shi'ite shrine, popular with both Iranian and Iraqi pilgrims.
Interior Minister Said Mohammed Sammour said the explosion, at a gas station, was not a terrorist act.
Sammour said one of bus' tires was overinflated, leading to the explosion that destroyed the vehicle. He said two workers and the bus driver were killed.
Security officials have launched an investigation and have closed off the area to journalists. Independent confirmation of the cause of the blast is unlikely. Syrian state media lagged several hours behind regional media in mentioning the explosion.
The incident coincided with a visit by Saeed Jalili, the head of Iran's Security Council.
Hilal Khashan - a political science professor at the American University of Beirut - says he believes Jalili's visit was to put pressure on the Syrian government.
"The Iranians are very much concerned that the Syrians are defecting from Iran's camp and tilting towards the moderate Arab governments and the U.S.," said Khashan.
Whether accidental or not, the blast is likely to add tensions to an already precarious relationship. Bomb attacks are rare in Syria, which has an extensive domestic intelligence apparatus. The last blast occurred in the same area in September, 2008.