Syria's foreign ministry on Sunday denounced accusations the government had deployed chemical weapons against a rebel-held town as an "unconvincing broken record".

"Allegations of chemical use have become an unconvincing broken record, except for some countries that trade with the blood of civilians and support terrorism in Syria," state news agency SANA quoted a ministry source as saying.

Damascus and its ally Russia have denied accusations that a toxic gas attack by Syrian troops left dozens dead in the rebel-held town of Douma.