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. The death toll is expected to rise because about 30 people were seriously wounded in the attack, the Observatory said.