Activists say Syrian government forces have attacked the rebel-held town of Moadamiyeh, southwest Damascus, with artillery fire as helicopters dropped barrel bombs.
A local media activist, identified as Ahmad, was quoted as saying that helicopters dropped more than 40 barrel bombs on the town and its surrounding areas on December 23.
The attacks come as opposition groups accused government forces of using poison gas in an assault there the previous night.
The Associated Press quoted Ahmad as saying five people died of suffocation following a missile attack late on December 22.
The Syrian Observatory for Human Rights said reliable sources in the area reported that those killed suffered "redness in the eyes, widening of the pupils, and bleeding in the lungs shortly after the shelling."
Amateur videos from a town clinic, made available on December 23, show medics intubating apparently unconscious patients.
They did not appear to have suffered traumatic injuries.
Washington could not confirm the attacks.