A US-backed Syrian force on Monday accused President Bashar al-Assad of opening the country's borders to "foreign terrorists" after he labelled its fighters "traitors".

"Bashar al-Assad and what's left of his regime are the last people with the right to talk of treachery," the Kurdish-dominated Syrian Democratic Forces said.

"It was the regime that flung the country's doors wide open to hordes of foreign terrorists from across the world."

Earlier Monday, Assad accused US-backed Kurdish fighters of being "traitors", ramping up the rhetoric against forces that control more than a quarter of the country.

Source: AFP