The question of how to deal with captured foreign fighters attracted wide attention last week with the capture of two British fighters by the Syrian Democratic Forces (SDF) – an alliance of militias dominated by the Kurdish YPG.
They are just two amongst hundreds captured in Syria and Iraq. Their growing number has become a major source of concern for the US, prompting American Defence Secretary Jim Mattis to urge allied nations to permit militants to return to their country of origin and face justice.
Mattis is expected to raise the issue of hundreds of foreign fighters that are amongst those captured by SDF during a meeting in Rome this week with other members of the coalition fighting with the Daesh group in both Syria and Iraq, according to CBS News.
The legal fate of the British pair held by SDF is not clear. The Guardian reported a senior Kurdish official who said that there had been no approach by Britain to extradite either man. "The SDF doesn't have a particular interest in the foreign jihadists," the official said. "These two were identified by the coalition forces after they were arrested.
Britain's position on its citizens fighting alongside Daesh is clear. Officials have consistently said that they would not allow militants travelling from the UK to join Daesh back into the country. Dozens had also been stripped of their British nationality on terrorism-related grounds since 2010 and it would appear that the same fate awaits the two British fighters.
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Guantanamo Bay may have been a potential destination, however, a US official, speaking on condition of anonymity, said the United States was in talks with the UK about what to do with them but at this point there were no plans to bring them to the United States or the US detention centre in Cuba.
The UK is not alone in refusing to allow foreign fighters back in to the country. The US has also been adamant and it's not at all clear why other nations allied to the US would permit the return of militants when the US is reluctant to do so.
Last September an American member who was allegedly fighting with Daesh in Syria surrendered to the SDF and was handed over to the United States' military custody in Iraq. The capture of a US national posed a serious dilemma for country. Trying American nationals in Military Commissions – like the military tribunals used to try Guantanamo detainees – is technically unlawful. But keeping the US citizens under SDF custody means that US is unwilling to follow its own advice.
Mattis is hoping to agree on a solution with his US partners. About a dozen members of the US-led coalition fighting Daesh will meet in Rome this week, where the defence secretary will emphasise the need for countries to take back foreign Daesh detainees.
"We are working with the coalition on foreign fighter detainees, and generally expect these detainees to return to their country of origin for disposition," Katie Wheelbarger, the principle deputy assistant secretary of defence for international security affairs, said.
US officials have expressed concerns about the lack of a clear path on how to deal with foreign fighters detained by the SDF.
The large number of detainees mixing in detention facilities often crammed with prisoners, could lead to a proliferation of militant views and deeper radicalisation, officials have said.
Read: US coalition will not target Daesh in Syria-government controlled areas
The other concern is SDF detention facilities reaching capacity. At one point, SDF forces were capturing 40 to 50 Daesh fighters, including Syrians, a day.
US officials say there are hundreds of foreign fighters and thousands of Syrian Daesh militants in SDF hands.
"The capacity problem is very real … I think they are willing to hold them as long as we need," Wheelbarger said.
"[But] if they continue to capture them at the rates that they are, their facilities are eventually going to be full."