More than 900 foreign fighters and 4,000 family members are believed to be held by Kurdish fighters in northern Syria.

The United States has called on European nations and other countries to repatriate and prosecute their citizens who travelled to Syria to join the Islamic State of Iraq and the Levant (ISIL, also known as ISIS).

The Kurdish-led Syrian Democratic Forces (SDF) say they have arrested more than 3,200 ISIL fighters in territory they control in northeastern Syria, with more than 900 believed to be foreign fighters.

In addition to the hundreds of men, the SDF also says it is holding more than 4,000 family members, including elderly people and young children.

“The United States calls upon other nations to repatriate and prosecute their citizens detained by the SDF and commends the continued efforts of the SDF to return these foreign terrorist fighters to their countries of origin,” State Department Spokesman Robert Palladino said in a statement on Monday.

The announcement comes just two days before foreign ministers of US allies are set to meet in Washington for talks on the anti-ISIL coalition, with questions on how to move forward without the military backing of the US.

The question of what to do with the foreign fighters in custody has grown increasingly thorny since US President Donald Trump‘s surprise announcement in December that he intends to withdraw all American forces from Syria.

Very few countries have expressed readiness to repatriate their citizens, posing a dilemma for the Kurdish-led forces, particularly lading up to the US withdrawal.

Security threat

Last week, France’s Interior Minister Christophe Castaner told French media that a handful of French fighters had already returned home and more would follow soon after the departure of American troops.

A French security source, speaking on condition of anonymity, told the AFP news agency that 130 people could be repatriated. A second French official said the group included 70 to 80 children held with their mothers.

However, Britain refuses to take back citizens who joined ISIL and has reportedly stripped them of their citizenship.

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El Shafee Elsheikh and Alexanda Kotey, two of the so-called “ISIL Beatles” – given the monikers by their hostages because of their English accents – are currently being held by the SDF.

The UK government stripped them of their British citizenship in 2014 and has said it has no legal obligations towards ISIL suspects.

Other European countries have remained largely silent about the fate of men and women whom many be seen as a security threat.

The campaign against ISIL is currently focused on a small, remote patch of land in eastern Syria, where thousands of civilians are trapped by the armed group.

ISIL declared a caliphate in 2014 after seizing large swathes of Syria and Iraq. The group established its de facto capital in the Syrian city of Raqqa.

However, ISIL has lost all their strongholds and the vast majority of the territory it controlled since then.

The war in Syria erupted started after an uprising against President Bashar al-Assad in 2011 was brutally repressed.

It has since morphed into a complex, multi-faceted war, with the UN estimating more than 400,000 deaths, millions of people displaced and much of the country’s infrastructure ruined.