By Con Coughlin of the Daily Telegraph
Turkey's military invasion of northern Syria raises some serious questions about the future status of up to 90,000 captives affiliated with Isis who are currently being held by Kurdish-led forces.
The principal objective of the Turkish offensive, which has been dubbed "Operation Peace Spring" by Turkish president Recep Tayyip Erdogan, is to clear Kurdish fighters from their bases along the Syrian border with Turkey.
Relations between Ankara and Kurdish separatist groups in northern Syria have been strained for decades, and Erdogan believes that, by establishing what he terms a "safe zone" in northern Syria, he can strengthen Turkey's defences against Kurdish terror groups that have used the area to launch attacks.
The offensive has been mounted at a time when the US-led effort to destroy the Islamic State of Iraq and the Levant (Isis) in Syria is winding down, with president Donald Trump keen to end America's military involvement ahead of next year's presidential elections.
Yet, at a time when there is already evidence that Isis is regrouping following its recent defeats in Iraq and Syria, concerns are being raised in Western security circles that the Turkish action means the Kurds may no longer be able to continue guarding captured Isis fighters, with the result that some may be able to escape and rejoin their jihadist comrades, thereby allowing Isis to rebuild its strength.
Although the majority of Isis fighters and their dependents are held in areas outside the area affected by the Turkish offensive, such as the al-Hol detention camp located in eastern Syria, the concern is that Kurdish fighters will be redeployed from guarding Isis detainees to help defend the Kurdish-controlled enclave.
Mazlum Abdi, the commander of the Kurdish-led Syrian Democratic Forces, has already announced that some of his forces tasked with securing the Isis prisoners were leaving for the border to do battle with the Turkish military.
The Turkish offensive certainly places European countries like Britain in an awkward position, particularly with regard to the estimated 2000 foreign Isis fighters that are said to be held in the camps.
These include several hundred who have links to Britain, such as Shamima Begum, who travelled from her home in east London to become an Isis bride and has had her British citizenship revoked by the Home Office.
The UK, in common with many other European countries, is refusing to repatriate citizens who went to fight with Isis, a policy that has caused dismay in Washington, where the Trump administration believes its European allies have a moral obligation to deal with the detainees.
At one point earlier this year an exasperated Trump threatened to dump the foreign fighters on the borders of the European countries from which they originated.
The prospect of some of these fighters being allowed to go free as a result of the Turkish incursion should certainly help to concentrate the minds of European politicians whose policy has essentially been to wash their hands of the Isis fighters' fate.
While EU officials will argue that tightened border controls will help to prevent Isis fanatics returning home, the notion that captured fighters, some of whom are accused of committing barbaric crimes, will be allowed to go free is not an option any Western government can countenance.
American officials have already taken a lead by transferring two of the so-called "Beatles" captured while fighting for Isis into US custody to prevent them escaping amid the current chaos on the ground in Syria.
London-born Alexanda Kotey,35, and El Shafee Elsheikh, a 31-year-old Briton born in Sudan, now face trial in the US on terrorism charges, which include the torturing and murder of Western hostages held during the caliphate's short-lived existence.
Britain and other European countries are likely to come under renewed pressure from Washington to take similar action against their nationals held in Isil camps.
It will certainly be hard, now that the security of captured Isis fighters can no longer be guaranteed, for European governments to persist with their current policy of abandoning the fighters to their fate.
It might save them the trouble of having to put Isis captives on trial in their home countries.
But if their failure to act results in Isis being able to rebuild its terrorist infrastructure, they will face even greater challenges in future years.