Dozens of Islamic State group fighters have surrendered in their former Syrian stronghold of Raqa, the US-led coalition said Saturday, as the fall of the one-time jihadist bastion nears.

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

A war monitor said no Syrian members of the jihadist group remained in Raqa, and that negotiations on the fate of foreign fighters were ongoing.

But the US-led coalition backing the offensive insisted that foreign fighters would not be allowed to leave the city.

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

In June, the US-backed Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab fighters, broke into Raqa, and since then they have captured around 90 percent of the city.

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

On Saturday, the US-led coalition confirmed dozens of IS fighters had handed themselves in.

"Within the past 24 hours, approximately 100 ISIS terrorists have surrendered in Raqa, and were removed from the city," the coalition said in a statement in response to AFP questions.

- Syrian IS fighters surrender -

Earlier, the Syrian Observatory for Human Rights, a Britain-based monitor of the war, reported that all the remaining Syrian IS members in the city had now left with their families.

"All Syrian fighters from the Islamic State group left Raqa over the past five days," said Observatory head Rami Abdel Rahman, saying they numbered around 200 fighters.

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

"They sent a message to the Raqa Civil Council (RCC) and to the tribal mediators," the official said. 

"Those that surrendered are local, not foreigners -- the foreigners have not handed themselves in yet," he said.

An SDF military source told AFP that buses and trucks were waiting outside Raqa and would take the surrendered fighters further east to Deir Ezzor province, much of which remains under IS control.

Members of the RCC -- a provisional administration for the city, set up by the SDF -- had been working with tribal leaders throughout the week to try to secure safe passage for civilians.

Up to 1,500 civilians have managed to flee the battle-ravaged city in the past week, according to the coalition. The United Nations estimates thousands more may still be trapped inside.

US-led coalition strikes have dropped off at points in the past week, with their latest update reporting no air raids on Friday.

- City on verge of capture -

Abdel Rahman said up to 150 foreign jihadists remain in Raqa and negotiations on their fate were ongoing.

"The foreign fighters are asking to leave in one group towards areas under IS control in Deir Ezzor province," in eastern Syria, he said.

The US-led coalition however insisted that "foreign fighters are not being allowed to leave Raqa," and cautioned that it still expected "difficult fighting in the days ahead."

And Nuri Mahmud, a spokesman for the key Kurdish People's Protection Units that forms the SDF's backbone, denied that any deal would be cut with IS.

"Daesh is on the verge of being finished in Raqa in the coming days," he told AFP, using the Arabic acronym for the group.

"Until this very moment, we are fighting Daesh."

IS captured Raqa in 2014, seizing it from other opposition forces, and turned it into the de facto capital of its "caliphate."

Under its rule, the city became synonymous with some of the worst of its abuses, including public executions, as well as a centre for the planning of attacks abroad.

The jihadists are also under attack in their remaining territory in Deir Ezzor province, where Syria's Russian-backed army on Saturday captured the town of Mayadeen.

The army and the SDF are fighting two separate campaigns in the province.

In neighbouring Iraq, the jihadists now hold just a sliver of territory in the Euphrates River valley.

Source: AFP