US-backed forces were on the brink of defeating the last remnants of the "Islamic State" (IS) group in the jihadists' de-facto Syrian capital of Raqqa on Saturday, according to officials close to the operation to retake the city.

A spokesman for the US-led coalition, Colonel Ryan Dillon, said that around 100 IS militants had already surrendered and been "removed" from the city since Friday.

"We still expect difficult fighting in the days ahead and will not set a time for when we think Islamic State will be completely defeated in Raqqa," he said.

But the Syrian Kurdish militia YPG told Reuters that coalition forces could have the city clear of IS forces within days.

Read more: Syrian Christians advance against IS in de-facto capital Raqqa

"The battles are continuing in Raqqa city. Daesh (IS) is on the verge of being finished. Today or tomorrow the city may be liberated," YPG spokesman Nouri Mahmoud said.

Kurdish YPG in Syrian SDF alliance

The YPG is one of the most influential militant in the Syrian Democratic Forces (SDF), an alliance of groups that also includes Arabs and Christian units.

The SDF offensive to retake Raqqa started in June with the help of US-led airstrikes and several hundred US special forces.

Syrian IS fighters leaving Raqqa

Hundreds of people are trapped in IS-held pockets in the city, raising concerns over civilian casualties and IS using human shields.

Local officials from the Raqqa Civil Council and tribal leaders announced Saturday they had struck a deal to evacuate civilians and local fighters. The SDF will search and screen all people departing Raqqa.

The US-led coalition confirmed the deal in a statement.

"The arrangement is designed to minimize civilian casualties and purportedly excludes foreign terrorists," the US-led coalition said in a statement, adding that it does not condone a deal that allows IS fighters "to escape Raqqa without facing justice, only to resurface somewhere else."

UK-based Syrian Observatory for Human Rights (SOHR) monitoring group said that the issue of foreign fighters was of particular concern.

"The obstacle to their departure is that the mastermind of attacks in Paris in November 2015 is believed to be among them and he has refused to surrender," SOHR head Rami Abdel-Rahman said. IS supporters killed 130 people in multiple terrorist attacks across Paris in November 2015.

Separately, the Syrian government and allied Shiite militia retook the town of Mayadeen from IS after intense fighting and Russian airstrikes, the Syrian military said Saturday.

Located along the Euphrates River near the Iraqi border, Mayadeen has been strategic IS stronghold as the group lost territory in Syria and Iraq.

Pro-Syrian regime forces have been trying to secure the Iraqi border and push IS out of a small pocket in the provincial capital Deir al-Zor

IS stronghold since 2014

IS had seized Raqqa as part of a broad offensive in Syria and Iraq in early 2014 and the city has since served as the jihadists' primary Syrian stronghold.

But IS has lost much of its territory after US and Russian-backed forces began separate offensives against the militant group. In July, US-backed Iraqi forces retook Mosul, the jihadists' de-facto capital in Iraq.

cw/amp/jm (Reuters, AP, dpa)