The spokesman for the US-led anti-Islamic State coalition says the Syrian Democratic Forces, a group comprising several factions but dominated by the Syrian Kurds, have moved back across the Euphrates River, to the east.
"The Syrian Democratic Forces have moved east across the Euphrates to prepare for the eventual liberation of Raqqa, Syria," the spokesman says on his Twitter feed, referring to Islamic State's de facto Syrian capital.
Turkish media quoted diplomatic sources as saying US Secretary of State John Kerry informed Ankara that this was taking place. However, a spokesman for the Kurdish People's Protection Units (YPG), was quoted by the Firat news agency as denying they planned to retreat.
If indeed the forces did retreat it remains unclear who holds the land west of the Euphrates, including the key city of Minbij, which the YPG-led forces recently seized from Islamic State.
Syrian rebels supported by Turkey and US-backed Syrian Kurdish forces clashed Thursday in the north of the country, activists and Kurdish officials said, raising fears of a new confrontation over territory amid a Turkish led intervention.
Syrian Kurds condemn the Turkish incursion into Islamic State-held Jarablus, calling it a "declaration of war."
US Vice President Joe Biden says the Syrian Kurdish forces his country backs must go back across the Euphrates River to the east bank.