The Britain-based Syrian Observatory for Human Rights says a government fighter jet carried out the strike Sunday in Halfaya in Hama province.
A man in the town told Reuters he could see "piles of bodies all over the ground," while another resident said people were trying to determine who died and who survived.
An amateur video released online shows more than a dozen dead or wounded people in rubble from a scene identified as a bakery in Halfaya. Free Syrian Army fighters from al-Farooq battalion claimed they had seized control of the town last week.
The human rights group says the 21-month-old uprising against Assad has now left more than 44,000 people dead.
The attack came as the main international envoy was beginning talks in Damascus aimed at ending the civil war. Lakhdar Brahimi was set to push for a negotiated solution to the conflict. Previous efforts have proved fruitless.