A Syrian rebel group accused government forces on Saturday of launching a deadly chemical attack on civilians in a rebel-held town 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 and said rebels in the eastern Ghouta town of Douma were in a state of collapse and spreading false news.
The U.S. State Department said it was monitoring the situation and that Russia should be blamed if chemicals were used.
The Syrian government has recaptured nearly all of eastern Ghouta from rebels in an offensive that began in February, leaving just Douma in the hands of an insurgent group, Jaish al-Islam.
Russian-backed Syrian government forces resumed the assault on Friday afternoon with heavy air strikes after days of calm.
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.
The political official of Jaish al-Islam said the chemical attack had killed 100 people.
Syrian state news agency SANA said the rebel group in Douma, Jaish al-Islam, was making "chemical attack fabrications in an exposed and failed attempt to obstruct advances by the Syrian Arab army," citing an official source.