A convoy will leave Syria's Raqqa on Saturday under an evacuation deal agreed as a US-backed force battles to seize Isil's last positions in the city.

The US-led coalition said the deal for the evacuation would exclude foreign Islamic State of Iraq and the Levant (Isil) fighters, but left unclear whether Syrian jihadists would be able to quit their one-time stronghold.

The agreement, reached by local officials, comes after days of talks on a way for the US-backed Syrian Democratic Forces to secure the last parts of the city while avoiding further civilian casualties.

Earlier Saturday, the US-led coalition said around 100 Isil fighters had surrendered to the SDF in the past 24 hours, but again stressed that no foreign fighters would be allowed to escape the city.

In neighbouring Deir Ezzor province meanwhile, Syria's army captured the Isil stronghold of Mayadeen, in the latest blow to the jihadists who are seeing their self-styled "caliphate" crumble.

Raqqa was once the de facto Syrian capital of the jihadist group's "caliphate" and the city's loss would be a new blow for Isil, which has already been driven from its strongholds in Iraq including second city Mosul.

In June, the US-backed SDF, an alliance of Kurdish and Arab fighters, broke into Raqqa, and since then they have captured around 90 percent of the city.

'Minimise civilian casualties'

In recent days, talks had been under way on a deal to secure the last parts of Raqqa while protecting trapped civilians, some of them being used by Isil fighters as human shields.

"The arrangement is designed to minimise civilian casualties and purportedly excludes foreign Daesh terrorists as people trapped in the city continue to flee the impending fall of Daesh's so-called capital," the coalition said, using the Arabic acronym for Isil.

"People departing Raqqa under the arrangement are subject to search and screening by Syrian Democratic Forces," it added.

A Raqqa official told AFP on Saturday that Syrian Isil members had surrendered overnight to the SDF, without specifying how many.