At least eight pro-Iran fighters were killed in US strikes on eastern Syria, a war monitor said Monday, after Washington announced the raids a day earlier in response to attacks on American forces.

The toll is "eight pro-Iran fighters dead, including at least one Syrian, and Iraqi nationals", the Syrian Observatory for Human Rights said, following the strikes late Sunday on the Mayadeen and Albu Kamal areas of Syria's eastern Deir Ezzor province.