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.
According to the UN more than 100,000 people have fled their homes since the offensive began on Wednesday.
President Erdogan says he wants to create a “safe zone” in northern Syria free of Kurdish militias which could also be home to Syrian refugees.
As the crisis deepened, US troops said they had come under fire from Turkish artillery on Friday.
What is the latest?
The Kurdish-led Syrian Democratic Forces (SDF) – a key US ally in the region – are facing numerous Turkish ground and air assaults along a stretch of the Turkey-Syria border about 75 miles (120km) long, correspondents say.
Dozens of fighters from the SDF and pro-Turkish factions have been killed. Turkey's military confirmed the first death of a Turkish soldier and said three others had been…
