There are unconfirmed reports that hundreds others are injured

The US is calling on Russia to end its support for the Assad regime after an alleged deadly chemical weapons attack in Syria.

It's thought to have killed at least 70 people - including many children - in Eastern Ghouta.

The US State Department's strongly condemned it - but the Syrian government's denied being responsible.

Mohamad Katoub, from the Syrian American Medical Society, says teams treated patients with symptoms suggesting chemical agents were used.

"Six of them died in the hospitals, their treatment didn't work. Then we started receiving details from the rescue teams that more patients are contaminated in their houses where the attack took place."

Russia dismissed the reports as 'fabricated'.

The reports come amid increased airstrikes targeting the rebel-held enclave of Douma.

Smoke rises after the Syrian army's shelling targeted the Douma district in Eastern Ghouta countryside of Damascus, Syria. Picture by: Ammar Safarjalani/Xinhua News Agency/PA Images

A spokesperson for UN chief Antonio Guterres said: "The Secretary-General is particularly alarmed by allegations that chemical weapons have been used against civilian populations in Douma.

"While the United Nations is not in a position to verify these reports, the Secretary-General notes that any use of chemical weapons, if confirmed, is abhorrent, and requires a thorough investigation."

The State Department in Washington said it was closely following the "disturbing reports" from the city of Douma in eastern Ghouta, which an aid group with links to opposition forces in the region said had been subjected to "one of the worst chemical attacks in Syrian history" late on Saturday.

There has been no independent verification of the claims, but the US has said that if they prove accurate they demand an "immediate response by the international community".