BEIRUT, Lebanon — Bombs that antigovernment activists said were dropped by a Syrian warplane on Sunday killed dozens of people at a bakery in the west-central town of Halfaya where residents had lined up for bread after the town received its first flour delivery in days.

The attack, and the number of casualties, could not be immediately confirmed. A local activist said he ran to the bakery soon after he heard a warplane and then explosions and the sound of ambulances. “There were bodies everywhere,” the activist, Samer, said.

Photographs he took after the attack showed bodies in a heap on a bloody sidewalk outside a low-slung building, which was damaged but still standing. Amateur video of what the activists said was the aftermath of the attack showed a man sitting near a motorcycle, his arm twisted around his back, struggling to stand as people around him screamed. Roughly a dozen people could be seen on the ground, covered in dirt or debris from the building; some were wounded, and several appeared to be dead. Armed men wearing camouflage outfits were helping to move the bodies, which were placed in bunches on truck beds.

The reasons for the attack were unclear, but activists speculated that it was a government response to the arrival in Halfaya of rebel fighters. The rebels occupied the town last week after embarking on a broad offensive to seize territory around the city of Hama, where the government has kept tight control after suppressing protests in the city last year. In days of fighting, civilians have been caught between the warring sides, a volatile development in a part of the country where members of Syria’s many sects live among one another in neighboring villages.