Turkey: U.S. says Syrian Kurds are pulling back in north Syria

ANKARA, Turkey -- Syrian Kurdish forces have started withdrawing east of the Euphrates River, Turkish officials said Thursday, a move that could fulfill a major demand by Ankara and the United States a day after Turkey sent in tanks across the border to help Syrian rebels take a key Islamic State stronghold.

The Turkish officials were quoting U.S. Secretary of State John Kerry, who relayed the news in a telephone conversation with his Turkish counterpart.

Turkey's surprise incursion Wednesday to capture the town of Jarablus was a dramatic escalation of Turkey's role in Syria's war. But Ankara's objective went beyond fighting extremists. Turkey also is aiming to contain the expansion by Syria's Kurds, who are backed by the United States and have used the fight against IS and the chaos of Syria's civil war to seize nearly the entire stretch of the border with Turkey in northern Syria.

U.S. Vice President Joe Biden flew into Ankara hours after the offensive was launched, and he backed Turkey with a stern warning to the Kurds to stay east of the Euphrates, which crosses from Turkey into Syria at Jarablus.

Kurdish forces "must move back across the Euphrates River. They cannot, will not, under any circumstance get American support if they do not keep that commitment," Biden said.

According to Turkish ministry officials, Kerry and Mevlut Cavusoglu discussed the Turkish military operation.

Kerry stressed the Syrian Kurdish forces "were in the process of retreating east of the Euphrates," the officials said, speaking on condition of anonymity in line with government regulations.

It was unclear Thursday whether Turkey-backed rebels who seized Jarablus on Wednesday would move against IS-held towns of nearby Kurdish-controlled areas, including the town of Manbij, which Kurdish forces retook from IS earlier this month. Manbij lies west of the Eurphrates, and Ankara has demanded the Kurds hand it over to Syrian rebels and withdraw.

On Thursday, Turkish forces were securing the area around Jarablus, Turkey's Defense Minister Fikri Isik said.