Turkish forces are stepping up air strikes and a ground offensive, as their incursion into Kurdish-held areas of northern Syria enters a second day.
Turkey’s military said it had seized designated targets. There are reports of heavy fighting in the central border region, and seven civilian deaths.
Tens of thousands of people are reported to be leaving their homes.
The assault on Kurdish-led forces, key US allies, follows US President Donald Trump’s decision to withdraw US troops.
Turkey says it wants to create a “safe zone” on the border for many of the Syrian refugees on its territory.
But on Thursday President Recep Tayyip Erdogan threatened to send the refugees to Europe instead if it characterised the Turkish offensive as an occupation.
On Wednesday, US Secretary of State Mike Pompeo denied the US had given Turkey a “green light” for the offensive.
In another development, two of the so-called “IS Beatles” have been taken out of Syria to “a secure location controlled by the US”, President Donald Trump has said.
El Shafee Elsheikh and Alexanda Kotey are accused of being part of an Islamic State group cell which kidnapped and murdered Western hostages in Syria.
The pair – who are from London – are in the custody of the American military, according to US media reports.
In a tweet, Trump described them as “the worst of the worst”.
In case the Kurds or Turkey lose control, the United States has already taken the 2 ISIS militants tied to beheadings in Syria, known as the Beetles, out of that country and into a secure location controlled by the U.S. They are the worst of the worst!
— Donald J. Trump (@realDonaldTrump) October 10, 2019
He said the decision to remove them from Syria had been taken “in case the Kurds or Turkey lose control”.