Thousands of civilians and "a large number" of former ISIS fighters have left one of the last areas held by the terror group in Syria, according to the U.S.-supported Syrian Democratic Forces (SDF).

Some 3,000 civilians left the area around the village of Baghouz in the last couple days by way of a humanitarian corridor established by the SDF, in advance of a possible siege against remaining ISIS forces in the town - said to total no more than a few hundred, according to an SDF spokesperson.

"Slowing down the offensive in #Baghouz yesterday, we managed to evacuate about 3.000 ppl from ISIS pocket through the corridor we opened. A large number of Daesh jihadists surrendered to our forces among the same group overnight," said a tweet from the SDF's Mostafa Bali.

The evacuations came after the U.S. cut back its involvement in operations around Baghouz, and continued plans to withdraw most of its troops from Syria. Under the terms of an apparent deal between President Donald Trump and his Turkish counterpart, Tayyip Erdogan, Turkey will step up its involvement in securing the area from an ISIS resurgence.

Several hundred U.S. troops will remain in Syria, according to recent reports, though they will be not as engaged in military operations.

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More than 10,000 people have reportedly left Baghouz in the last several weeks, many of them dramatic stories of what life was like under repressive ISIS rule. Civilians have been evacuated to a camp for displaced persons in the north. The ISIS fighters who surrendered are being moved to detention facilities.

But it's not clear what will happen to the ISIS fighters in the long term. There's a particularly challenging issue with fighters from other countries who joined ISIS, and whose home nations now no longer want them back. Among those being held by the predominately Kurdish SDF forces are citizens of Western European nations and the United States.

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Retaking the last ISIS-held enclave in Baghouz would be a milestone in the four-year campaign to end the group’s self-proclaimed caliphate that once covered a vast territory straddling both Syria and Iraq. Some experts, however, are warning of a return of ISIS forces following any U.S. departure, or any power or territorial vacuum that might be created in the future.

The U.S.-backed SDF – which Turkey strongly opposes because of its link to the separatist Kurdistan Workers Party (PKK) - is so far not part of ongoing U.N.-led talks to end the Syrian conflict, U.N. officials have said. There is concern the Turks will move against the SDF once the U.S. departs, though Trump administration officials have called for the Kurds to be protected.

The Associated Press contributed to this report