More than 20 people were killed when Syrian rebels shelled a tent being used for election campaigning in the southern province of Deraa, a monitoring group said on Friday.
At least 11 civilians, including a child, were among those killed in the attack which occurred in the al-Matar district of Deraa city on Thursday night, the Britain-based Syrian Observatory for Human Rights said.
Syria is holding an election next month that looks all but certain to give President Bashar al-Assad a third seven-year term. His opponents have dismissed the vote as a farce, Reuters reported.
Images shared by anti-Assad activists online purportedly of the attack showed a burst of flame on a city street at night as people ran or stood nearby. The photographs could not be independently verified.
The death toll is expected to rise because about 30 people were seriously wounded in the attack, the Observatory said.
More than 160,000 people have been killed in Syria's three-year-old conflict, according to the Observatory, which monitors violence on both sides through a network of sources in the country. Millions more have fled their homes.