A Syrian government air strike northeast of Damascus killed about 80 people on Saturday, rescue workers and the Syrian Observatory for Human Rights said.
At least 200 more people were wounded in the attack, which struck a market place in Douma, about 15 km (10 miles) northeast of Damascus, the British-based Observatory and the local arm of the Syrian Civil Defense, which operates in rebel-held areas, said.
A Syrian military source said the air force had carried out air strikes in Douma and the nearby area of Harasta, saying these had targeted headquarters of the rebel group Islam Army.
The Observatory said at least 10 rockets were fired during the attack, and accused the warplanes of bombing again after rescue workers had arrived at the scene.
"This is a documented massacre," said Rami Abdulrahman, who runs the Observatory.
On Saturday, the Islam Army insurgent group attacked government positions in Harasta.
(Writing by Tom Perry; Editing by Dale Hudson)