The U.S. is urging Turkey not to undertake an offensive into northeastern Syria against U.S.-backed Kurdish forces that helped to defeat the Islamic State and that are now maintaining prisons with thousands of the terror group's fighters.

An American military delegation is in Turkey to meet with Turkish officials and continue negotiations on an alternative to a Turkish military operation that could also threaten U.S. troops stationed in the area.

Turkish President Recep Tayyip Erdogan, who has a close relationship with President Donald Trump, announced Sunday that Turkey's military would begin the offensive imminently against the Syrian Democratic Forces (SDF), the mostly Kurdish group that served as the U.S. ground troops in the fight to destroy ISIS's caliphate in Syria. The group has ties to their Kurdish counterparts in Turkey, the Kurdistan Workers' Party or PKK, which the U.S. and Turkey consider a terrorist organization.

Read more: ABC News