A day after Turkish tanks crossed the border into northern Syria, most of a U.S.-backed largely Kurdish army has moved east of the Euphrates River on Thursday, according to a U.S. military spokesman.

Turkey and Vice President Joe Biden had called on the Kurds to leave Arab lands in Syria and return east of the Euphrates to traditional Kurdish territory. Biden threatened to cut off supplies to the Kurds if they didn’t fall back.

Some of the Syrian Democratic Forces remained in the region to remove roadside bombs, U.S. officials added.

The United States is supporting the Turkish military operation with airstrikes and conducted at least eight against ISIS targets on Wednesday, according to a senior defense official.