Turkish Foreign Ministry says U.S. Secretary of State John Kerry has told his Turkish counterpart that Syrian Kurdish forces have started withdrawing east of the Euphrates River.

The pullback was a major demand by Ankara after Turkey sent in forces across the border to take a key Islamic State stronghold the previous day.

Turkish ministry officials say Kerry and Mevlut Cavusoglu spoke by telephone on Thursday. Turkey's incursion into northern Syria was also meant to contain an expansion by Syria's Kurds.

Battling IS militants in Syria, the U.S.-backed Syrian Kurds have been able to seize nearly the entire stretch of the border with Turkey in northern Syria.

Vice President Joe Biden warned on Wednesday that the Syrian Kurdish forces will lose U.S. support unless they retreat east of the Euphrates.