(CNN) President Donald Trump is ordering the remaining US forces out of northern Syria, Defense Secretary Mark Esper said Sunday, a development that has paralyzed the fight against ISIS and ceded US and Kurdish battlefield gains to Moscow and Damascus.

"We have American forces likely caught between two opposing, advancing armies and it's a very untenable situation. I spoke with the President last night, after discussions with the rest of the national security team, and he directed that we begin a deliberate withdrawal of forces from northern Syria," Esper said on CBS' "Face the Nation." "Which is where most of our forces are."

In explaining the decision, Esper also said that "in the last 24 hours" the US had learned that America's primary ally in the fight against ISIS, the Kurdish-led Syrian Democratic Forces, were "looking to cut a deal" with the Syrian regime and their Russian backers in order to "counter attack against the Turks in the north," something the SDF leadership had told America it would do in the absence of US assistance in the face of Turkish attacks.

Despite Esper saying the US only learned of the effort in the last 24 hours, CNN has reported that the SDF commander told a senior US diplomat Thursday that this was his intent.

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