DAMASCUS - The Islamic State group has lost its Syrian stronghold Raqa, but the fate of hundreds of its foreign fighters who had been expected to battle to the death remains a mystery.
Captured by IS in 2014, the city became a "terror capital," where the jihadists carried out some of their most gruesome abuses and also planned devastating foreign attacks, like the Paris massacres of 2015 and August's Barcelona attack.
Who were the IS fighters in Raqa? -
After the 2014 declaration of its self-styled "caliphate" straddling Syria and Iraq, thousands of local and foreign fighters flocked to the jihadist group's ranks, with Raqa becoming its de facto Syrian capital.
US officials estimated as many as 40,000 fighters travelled to join the jihadists over the years, dispersed across a territory that was once the size of Britain.
In Raqa, the jihadists put up a fierce fight after the US-backed Syrian Democratic Forces broke into the city in June.
But in four months the SDF seized around 90 percent of the city, and fewer than 1,000 Syrian and foreign fighters were left in their onetime stronghold.
- Where did the fighters go? -
Senior IS commanders are believed to have left Raqa before the SDF penetrated the city, and hundreds of its fighters were killed in clashes with the SDF and in US-led coalition strikes.
As the battle neared its final phase, local officials negotiated a deal that saw several hundred Syrian IS fighters surrender with their relatives to the SDF forces.
The Raqa Civil Council that negotiated the deal, as well as the US-led coalition, insisted no foreign fighters were among those who surrendered over the weekend.
Before the end of fighting, the coalition and SDF officials had estimated hundreds of diehard, mostly foreign fighters remained in the city.
But there was no public sign that those fighters had either surrendered en masse or been killed in the last 24 hours of fighting for the city.
The Syrian Observatory for Human Rights, a Britain-based monitor of the war, said a group of 130-150 foreign fighters had turned themselves in before the end of the battle.
"They surrendered the day before yesterday," said Observatory director Rami Abdel Rahman.
"They were turned over directly to foreign intelligence services, the French for example," he added, citing sources on the ground.
Abdel Rahman said the group included Arabs from outside Syria, as well as Europeans and nationals from central Asian countries.
Other reports suggested a convoy of foreign fighters had been able to escape the city towards IS-held territory in neighbouring Deir Ezzor province, a claim denied categorically by SDF officials.
SDF spokesman Talal Sello said fighters that were not included in the surrender deal either "turned themselves in afterwards or were killed."
"We're doing clearing operations and searching for sleeper cells, there could be terrorists hidden here or there," he added.
Coalition spokesman Colonel Ryan Dillon told AFP that an additional 100 IS fighters had surrendered in the last 24-48 hours, and screening had uncovered four foreign fighters among them.
He could not specify which countries they were from.
- What happens to the fighters? -
Dillon denied reports that the coalition was holding any fighters.
"That is not something that we have done," he said.
"We have coalition forces that will interrogate them and ask them to try to get information from them, but they are in SDF control."
Under the deal negotiated by local officials, Syrian IS fighters who surrendered have been biometrically registered and turned over to local tribal leaders who will "be responsible for them and vouch for them," he added.
The SDF is expected to contact the home countries of any foreign fighters it holds, to discuss the possibility of turning them over to face prosecution.
In September, the SDF turned over an American IS fighters to US officials and he is now being held in Iraq.