Fierce fighting is taking place around the Syrian border town of Ras al-Ain as Turkish forces continue their offensive in the north-east against the Kurds.
Turkey says it has taken the key town, but the Kurdish-led Syrian Democratic Forces (SDF) disputes this.
Turkey has also denied targeting US forces after the Pentagon said troops further west had come under fire.
Nearly 50 civilians have reportedly been killed on both sides of the border and 100,000 displaced since Wednesday.
President Donald Trump’s decision to withdraw US troops from the area effectively triggered the Turkish incursion against the SDF – the main Western allies in the fight against the Islamic State (IS) group.
Turkey accuses the Kurds of being terrorists and says it wants to drive them away from a “safe zone” inside Syria where it plans to resettle more than three million Syrian refugees currently in Turkey.
One major concern for the international community is the fate of thousands of suspected IS prisoners, including many foreign nationals, being guarded by Kurdish-led forces in the region.