The Kurdish-led Syrian Democratic Forces (SDF) currently hold thousands of suspected IS prisoners.
Areas in north-eastern Syria under SDF control have come under heavy bombardment from Turkey since it launched its offensive on Wednesday.
More than 50 civilians have reportedly died on both sides of the border.
Turkey accuses the Kurds of being terrorists and says it wants to drive them away from a "safe zone" reaching some 30km into Syria.
It also plans to resettle more than three million Syrian refugees in the zone who are currently in Turkey.
According to the UN, more than 100,000 people have ...
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