France warns Turkey against 'any initiative' threatening fight against IS in Syria

France urged Turkey on Monday to "avoid any initiative" that could harm the fight against the Islamic State group in Syria, as Ankara vows to press ahead with a long-threatened offensive against Kurdish forces.

The US has announced that it will pull back from key positions along Syria's northern border, paving the way for Turkey to intervene against Kurdish militants that it regards as terrorists.

Turkish President Recep Tayyip Erdogan has warned the operation against the Kurds, Washington's main ally in the battle against IS, could come "any night without warning".

"We call on Turkey to avoid any initiative that would run counter to the interests of the global coalition" fighting IS in Syria, the French foreign ministry said in a statement.

Turkey is a member of the US-led international coalition.

The ministry also insisted that captured European jihadists in Syria's northeast remain in "safe detention".

The White House has said Ankara will be responsible for IS fighters captured and held in Kurdish detention centres.

Turkey wants a "safe zone" in northern Syria -- 30 kilometres deep and 480 kilometres (300 miles) wide -- that would push the Kurdish People's Protection Units (YPG) militia away from its border.

It says the buffer zone would also allow for the return of some of the 3.6 million Syrian refugees in Turkey, where anti-refugee sentiment is growing.

Erdogan's spokesman tweeted on Monday that Turkey "will not allow (IS) to return in any shape and form".