In a tiny sliver of land along the Euphrates River in northern Syria, about 300 battle-hardened ISIL fighters are making a last stand, with just a "few days" remaining for the group's total military defeat, according to US-backed Kurdish forces battling the fighters.

But US President Donald Trump - even while hailing an impending "100 percent victory" - has issued a threat that, if executed, could help the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group rise once again. 

In a flurry of tweets on Sunday, Trump demanded that his European allies "take back over 800 ISIS fighters we captured in Syria and put them on trial". The alternative, he threatened, "is not a good one in that we will be forced to release them".

If Europe fails to deal with the issue, ISIL could "permeate" the continent, he said, calling on Britain, France and Germany to "do the job they are so capable of doing".

The slow-rolling crisis over foreign ISIL prisoners in Syria has taken on a new urgency, analysts say, because of Trump's recent vow to pull US troops out of Syria. 


US troops withdrawal from Syria 'will be gradual' process (1:52)

The announcement in December shocked US allies, prompting concern that an ill-planned withdrawal could lead to an ISIL resurgence. It also alarmed the US-allied Syrian Democratic Forces (SDF), the Kurdish-led troops battling ISIL in northeastern Syria, as the move increases the possibility of an assault on their territory by Turkey. Ankara considers the SDF's main YPG militia a terrorist organisation.

The SDF played a key role in the US-led coalition's military offensive to drive ISIL out of cities and towns in eastern Syria, including Raqqa, the former capital of the group's self-declared caliphate. In the process, the SDF captured thousands of ISIL fighters, detaining them in makeshift prisons around Ayn Issa in the Raqqa district and holding their children and wives in detention camps.

"We currently have thousands of foreign ISIS fighters and their family members, and it's a big logistical problem," said Kino Gabriel, spokesperson for the SDF.

"It's a big burden," he said, arguing that the self-imposed Kurdish administration in the region does not have the capacity to "secure the prisons and prevent ISIL fighters from escaping" or provide services to the women and children in their custody.

More than 1,000 ISIL prisoners in SDF detention were from Europe, he said, a number that amounts to a sixth of the total number of Europeans who left the continent to join the armed group, according to figuresfrom the US-based think-tank The Soufan Group.

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The nearly 6,000 Europeans were among some 30,000 foreigners who arrived in the Middle East after ISIL declared its caliphate in Iraq's second largest city of Mosul in 2014.

At its peak, the group controlled an area equivalent to the size of the United Kingdom, but following a military offensive against it by a US-led coalition in Syria and Iraq, ISIL lost nearly all of its territory and is now confined to the enclave in Baghouz village on the Euphrates.

'Extremely difficult' 

The fighters and their families,captured by SDF, are stuck in limbo, unwanted by their home countries and unlikely to receive a trial by the SDF, an armed group that Gabriel said did not have "the authority or the capacity" to prosecute detainees or hold them long-term.

While Gabriel did not comment on the number of detention centres holding ISIL fighters, the New York Times, quoting anonymous US and SDF officials, put the number at seven. Most of these temporary facilities, located around Ayn Issa, are former schools and old government buildings.

In addition to the makeshift prisons near Raqqa, there were at least four detainee facilities located near US army bases in the provinces of Deir Az Zor and Hasakah, said Abdulnasser al-Ayed, a Syrian journalist who reports on the issue. 

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The US and the SDF have long urged European allies to take back ISIL fighters, and Gabriel said talks with European countries have been "ongoing for more than two years".

But previous negotiations have ended without agreement, and only a handful of ISIL detainees - mostly women and children - have been repatriated to their countries of origin.

On Monday, Trump's demand on fighters' repatriation was rejected by several countries in Europe, where returning ISIL members have carried out deadly assaults, including the 2015 attacks in Paris that killed more than 130 people, and the bombings in Brussels the next year that left 32 dead.   

A spokesperson for British Prime Minister Theresa May reiterated the UK's stance that foreign fighters must be brought to justice "in the region where the crimes had been committed". In France, which has taken the same stand as Britain, Justice Minister Nicole Belloubet told France 2 television that her government was "not changing our policy".

And Heiko Maas, Germany's foreign minister, told reporters in Brussels that organising repatriation of foreign fighters will "be extremely difficult" and said they can only "return if it is ensured they can immediately be taken into custody". Insufficient evidence

European governments would "prefer to delay the return [of ISIL recruits] or otherwise push the burden on others", said Robert Wesley, president of the Austria-based Terrorism Research Initiative.

Outlining the factors for European reluctance, he said: "Firstly, public opinion is generally negative. Secondly, large numbers can quickly overwhelm judicial and security resources, especially if evidence of a committed crime is scarce or ambiguous and there is a prospect of an early release into the public."

The SDF said it did not have the capacity or the resources to conduct interrogations and obtain the information needed to ensure successful prosecution. Gabriel, the SDF spokesperson, also said many of the fighters in their custody had lived and fought mainly in Iraq.


Hundreds of women, children held as ISIL loses last Syria bastion (3:28)

Insufficient evidence could result in many fighters walking free from European prisons within a few years of their return, said Martin Reardon of The Soufan Group. European countries faced a "real dilemma", he said, noting: "You can't say just because they were there and captured, they were a fighter."

For a case against an ISIL returnee to stand in a European court, "You need witnesses or the person's own testimony in court, or some sort of evidence to support that case," he said.

"If not, you have no recourse but to let them go … and if radicalised terrorists are set free and go on to stage attacks, the cost will be devastating."

Meanwhile, the likelihood of rehabilitating someone who was "involved in combat and killing is very slim", Reardon said, adding that conducting surveillance on freed ISIL detainees would be impossible because of the high cost involved. International tribunal

Despite European reluctance to take back ISIL detainees, keeping them in SDF prisons and camps is not a long-term solution, said analysts. ISIL could attack such facilities to free detainees, especially in the confusion of a US withdrawal or the chaos of a Turkish assault on the region.

"ISIS has a tradition of brazen and unexpected attacks on critical facilities, including prisons. Even if the US maintains a presence in northern Syria and supports the protection of prison facilities, such concentrations of fighters would continue to present a tempting target," said Wesley of the Terrorism Research Initiative.

Al-Ayed, the Syrian journalist, agreed. Predicting an attack "very soon", he said: "They [ISIL] will want to free prisoners, especially with active cells in and around the area and with the US troop withdrawal looming."

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If the Europeans refused to take back the ISIL detainees, the SDF could hand them over to the Syrian government. But in such a scenario, the Syrian government could "expose detainees to the most severe torture to obtain information," said Nawaf Khalil, director of the Germany-based Centre for Kurdish Studies.

Others said the government was also likely to execute ISIL fighters, even though the European Union opposes the death penalty.

Khalil said the only remaining option was to set up an international court to consider each detainee's case with the aim of repatriating them after a trial.

Gabriel, the SDF spokesperson, said talks with the coalition and the US army to set up such a system were under way.

"This court can take responsibility for the interrogation of those terrorists and to take all the information needed from their countries to be able to prosecute them … and then give them the sentences that they need or deserve for the crimes that they have committed."

For now, despite Trump's threat, the SDF does not plan to release its ISIL prisoners. 

"We know the terrifying things and the crimes they have committed against the people of Syria and Iraq," Gabriel said. "It is in our best interest not to let them go because we faced the horrors that they're capable of and we don't want it to happen to any other human being."


INSIDE STORY: What should be done with foreign ISIL fighters captured in Syria? (26:01)

Source: aljazeera.com