Pressure is building in the US to stop Turkey continuing its offensive against Kurdish-held areas in Syria.
Defence Secretary Mark Esper warned of “serious consequences” while Treasury Secretary Steven Mnuchin held out the prospect of fresh sanctions.
President Donald Trump’s decision to withdraw US troops effectively triggered the Turkish incursion.
He has said he would like the US to negotiate a truce between Nato ally Turkey and the Kurds.
Turkish President Recep Tayyip Erdogan, however, says the military operation will continue. Kurdish leaders accuse the US of stabbing them in the back.
Meanwhile, the Pentagon said US forces near the town of Kobane – which were not included in the US withdrawal – had come under Turkish artillery fire on Friday evening.