A Syrian rebel group has accused government forces of dropping a barrel bomb containing poisonous chemicals on civilians in Eastern Ghouta, and a medical relief organisation said 35 people had been killed in chemical attacks on the area.

Syrian state media denied government forces had launched any chemical attack as soon as the reports began circulating and said rebels in the Eastern Ghouta town of Douma were in a state of collapse and spreading false news.

The US State Department said reports of mass casualties from an alleged chemical weapons attack in Douma were "horrifying" and would, if confirmed, "demand an immediate response by the international community".

The Syrian Observatory for Human Rights said 11 people had died in Douma as a result of suffocation caused by the smoke from conventional weapons being dropped by the government. It said a total of 70 people suffered breathing difficulties.


Rami Abdulrahman, the Observatory director, said he could not confirm if chemical weapons had been used.

Medical relief organisation Syrian American Medical Society (SAMS) said a chlorine bomb hit Douma hospital, killing six people, and a second attack with "mixed agents" including nerve agents had hit a nearby building.

Basel Termanini, the US-based vice president of SAMS, told Reuters the total death toll in the chemical attacks was 35.

"We are contacting the UN and the US government and the European governments," he said by telephone. Reuters could not independently verify the reports.

Syrian government forces pressed their offensive against the last rebel-held town in Eastern Ghouta near the capital Damascus under the cover of airstrikes as shelling of civilian areas on both sides claimed more lives, state media and opposition activists said.

Syrian government forces resumed their offensive on rebel-held Douma after a 10-day truce collapsed over disagreement regarding evacuation of opposition fighters. Violence resumed days after hundreds of opposition fighters and their relatives left Douma towards rebel-held areas in northern Syria.

A reporter for Lebanon's Al-Manar TV embedded with Syrian troops near Douma said government forces advanced towards Douma from the towns of Misraba and Madiara that were recently captured by troops. Al-Manar TV is run by Lebanon's Hizbollah group that has sent thousands of fighters to Syria to back government forces.

In this photo released by the Syrian official news agency SANA, shows a man receiving treatment at a hospital in Damascus, Syria. Photo / AP
In this photo released by the Syrian official news agency SANA, shows a man receiving treatment at a hospital in Damascus, Syria. Photo / AP

The government-controlled Syrian Central Military Media said government forces captured several farms on the southern and western edges of the city that is home to tens of thousands of people. SCMM said the area controlled by the Army of Islam in and around Douma is 19 sq km.

The group said its fighters repelled all government attacks, adding that 17 Syrian soldiers were killed.

State media was reported that troops are approaching Army of Islam fortifications on the edge of the town adding that street battles could begin soon.

It said warplanes bombarded the group's headquarters and command and control centre.

State TV said Army of Islam fighters pelted several neighbourhoods in Damascus with mortar shells killing six civilians and wounding more than 30.

- Reuters, AAP, AP