Defense Secretary Mark Esper said on CBS' "Face the Nation" on Sunday that the U.S. is preparing to relocate 1,000 troops from northeastern Syria as fighting between Turkish-backed forces and Syrian Kurdish fighters escalates.

"In the last 24 hours, we learned that [Turkish forces] likely intend to expand their attack farther south than originally planned, and to the west. ... We also have learned the last 24 hours that the Kurdish forces, the SDF, are looking to cut a deal with the Syrians and the Russians to counterattack against the Turks in the north. So we find ourselves, as we have American forces likely caught between two opposing, advancing armies and it's a very untenable situation."

— Mark Esper

Driving the news: Esper made the announcement as Turkish-backed forces seized positions along a highway that serves as the U.S. military's main supply route into Syria, forcing U.S. troops to withdraw from another town in the northeast, according to the Washington Post.

U.S. and Kurdish officials told the Post that Turkish-backed rebels have set up checkpoints on the highway near Ain Issa, which potentially cuts off U.S. troops based to the west — in Manbij and Kobane — from the bulk of the U.S. forces farther east.

The highway is also a route for aid. Humanitarian organizations are withdrawing staff from northeastern Syria as the fighting continues, aid workers said.

Syrian Kurdish officials on Sunday said 950 Islamic State, or ISIS, supporters had escaped from a camp for displaced people near a U.S.-led coalition base amid clashes near Ain Issa, a key Kurdish-held town in northern Syria.

The big picture: Esper, appearing on "Fox News Sunday," was grilled by Chris Wallace about reassurances he made last week that the U.S. was not abandoning their Kurdish allies, who lost more than 10,000 troops in the fight against ISIS. The head of the primarily Kurdish SDF said Sunday that the U.S. was leaving them to be slaughtered.

Esper responded: "I would say what we've been saying, because we stay in contact with them. We're doing everything we can to get the Turks to stop this egregious behavior. Get them to go back across the line and stop. And that's our message to them at this point in time."

"I would say what we've been saying, because we stay in contact with them. We're doing everything we can to get the Turks to stop this egregious behavior. Get them to go back across the line and stop. And that's our message to them at this point in time." Trump, meanwhile, tweeted on Sunday morning: "Do you remember two years ago when Iraq was going to fight the Kurds in a different part of Syria. Many people wanted us to fight with the Kurds against Iraq, who we just fought for. I said no, and the Kurds left the fight, twice. Now the same thing is happening with Turkey. The Kurds and Turkey have been fighting for many years. Turkey considers the PKK the worst terrorists of all. Others may want to come in and fight for one side or the other. Let them! We are monitoring the situation closely. Endless Wars!"

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