The source said Kerry had told Foreign Minister Mevlut Cavusoglu in a telephone call Thursday morning that PYD units were moving to the east of the river.
Ankara has long insisted that the PYD and its military wing, the YPG, should not retain a presence west of the Euphrates. The group — the Syrian affiliate of the PKK, which has waged war on Turkey for 32 years — had established a foothold in the region after helping capture the city of Manbij from Daesh earlier this month.
Kerry’s conversation with Cavusoglu came after Turkey helped the Free Syrian Army (FSA) liberate Jarabulus from Daesh on Wednesday.
The top U.S. diplomat said the PYD was in the process of pulling back to the east of the Euphrates and underlined Washington’s ongoing cooperation with Ankara over Syria.
During a visit to the Turkish capital on Wednesday, U.S. Vice President Joe Biden pledged the PYD would retreat or the U.S. would sever ties with the group, which is called a terrorist organization by Turkey.
Operation Euphrates Shield was launched early Wednesday and by evening the FSA — backed by Turkish tanks, artillery and air power, as well as aircraft from the U.S.-led anti-Daesh coalition — had taken the city, which lies around a kilometer (mile) from the Turkish border.