Turkey will not back NATO Baltic defences
NATO leaders are due to meet in London for a summit, where they are supposed to discuss security concerns in the Baltics and Poland, where the members will agree to defend the countries if Russia attacks.
Turkey has accused NATO of dismissing its own concerns about Kurdish fighters.
The US and other European countries have backed the Kurdish-dominated Syrian Democratic Forces (SDF) in the fight against the Islamic State group.
Turkey considers the Syrian-Kurdish fighters to be terrorists and has launched an offensive into northern Syria against them.
Kurdish-led Syrian forces expelled IS from its last patch of land in March, but the jihadists have continued to claim deadly attacks.
Meanwhile, dozens of Syrian refugees were returned from Turkey on Friday in the first reported repatriations to the area targeted by Ankara's offensive against Kurdish forces last month, state news agency Anadolu said.
Around 70 Syrians, including women and children, crossed from Ceylanpinar in Turkey to Ras Al-Ayn in Syria, Anadolu reported.
Muazzin al Mohammed, one of the refugees, said he had been living in Turkey for seven years, adding: "We are happy to return to our homeland. I was 11 years old when I left Ras Al-Ayn."
Read more: Some Syrians are fleeing Turkey’s offensive, others are returning home
Turkey's defence ministry said on Thursday that around 200 people had returned to the Syrian town of Tal Abyad from another part of northern Syria now that Kurdish militants had been cleared.
But analysts have cast doubt on President Recep Tayyip Erdogan's claims that Turkey can repatriate up to two million Syrians to a "safe zone" being created in the north of the country.
Turkey is home to some 3.6 million Syrian refugees, more than any other country.