Syrian opposition activists say government helicopters are dropping barrel bombs and firing rockets on a flashpoint town southwest of Damascus in attacks that killed five people.

A media activist based in Moadamiyeh says the five people all died of suffocation, accusing the government of firing four rockets loaded with "poison gas" in an attack Tuesday night.

The activist who identifies himself by his first name, Ahmad, said the barrel bomb attacks have continued through Wednesday amid clashes in the town.

The claim of a poison gas attack could not be independently verified. It was also reported by the Local Coordination Committees group and the main Western-backed Syrian National Coalition opposition group.

Moadamiyeh was the site of a 2013 chemical attack on rebel-held areas outside Damascus that killed hundreds of people.