Turkey Starts Repatriating Captured ISIS Fighters

Turkey plans to deport suspected ISIS fighters, including a German and a Danish national, according to the Anadolu News Agency. President Erdogan stated that Turkey holds around 1200 suspected ISIS militants, many from Europe. Despite Turkey's threats to deport them, European countries refuse to take them back, having revoked their citizenship. Turkey's military actions in northern Syria, following the withdrawal of U.S. troops, have raised concerns about the fate of these prisoners.

What action did Turkey take in northern Syria that affected the situation with ISIS fighters?

What concerns have been renewed regarding the fate of the prisoners?