The US has called on Russia to end its support for the Syrian regime after at least 70 people were killed in an alleged chemical attack.

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.

As well as the dead, more than 500 other civilians were injured in the strike, the Union of Medical Care and Relief Organisations (UOSSM) told Sky News.