The US will step aside for an imminent Turkish operation against Kurdish-led forces in north-eastern Syria, the White House has said, in a major shift.
Turkey wants to clear Kurdish militiamen – whom it regards as terrorists – away from the border.
The Turks would become responsible for all Islamic State (IS) group prisoners in the area, the US statement said.
Kurdish YPG fighters have until now received strong support from the US, which has hundreds of troops in Syria.
In January, President Trump threatened to “devastate Turkey economically” if it attacked Kurdish forces following a planned US pullout from Syria.
However, the White House statement issued on Sunday makes no reference to the YPG, which has played a leading role in defeating IS – also known as Isis – in Syria.
The statement followed a phone call between President Donald Trump and Turkish President Recep Tayyip Erdogan.