The last remaining Isis fighters in the group's self-styled "capital" Raqqa are expected to leave the city on Saturday night, taking civilians with them as human shields, according to reports.

In a withdrawal agreed with US-backed Syrian militias that have them surrounded, Syrian Isis fighters will leave the city on Saturday evening.

Officials gave conflicting accounts on whether foreign fighters would also be leaving the city, where the Syrian Democratic Forces (SDF) have been battling to defeat Isis since June.

​SDF spokesman Talal Silo said any fighters who were not signed up to the deal that allows them to leave Raqqa would be left behind "to surrender or die”.

Omar Alloush, a member of Raqqa's Civil Council, said the evacuation would include foreign fighters. He said it would take place overnight into Sunday. The jihadists would be taking some 400 civilians with them as human shields, he said.

The final defeat of Isis in Raqqa would be a milestone in efforts to roll back the theocratic "caliphate" the group declared in 2014 in Syria and Iraq, where earlier this year it was driven from the city of Mosul.

Isis used Raqqa as a base to plan attacks against the West.

Woman celebrates after being rescued from Isis in Raqqa

The US-led coalition against Isis said a convoy was due to leave Raqqa on Saturday, in an arrangement agreed by local parties.

It described the arrangement as "a civilian evacuation" and said it would not condone any arrangement that allowed "terrorists to escape Raqqa without facing justice".

The coalition statement said the arrangement brokered by the Raqqa Civil Council and local Arab tribal elders on Oct. 12 was "designed to minimise civilian casualties and purportedly excludes foreign Daesh terrorists".