Ankara: The Turkish military says it has killed at least 260 Syrian Kurdish fighters and Islamic State militants in the first four days of an offensive into the Kurdish-dominated Afrin region of north-west Syria.

The air and ground operation launched on Saturday has opened a new front in Syria's multi-sided civil war and could threaten US plans to stabilise and rebuild a large area of north-east Syria - beyond President Bashar al-Assad's control - where Washington helped a force dominated by the mainly Kurdish YPG, to drive out Islamic State militants.

A Turkish journalist takes a selfie with Turkish soldiers on the border with Syria on Monday. Operation Olive Branch on the Kurdish enclave of Afrin started on Saturday. Credit:Lefteris Pitarakis

The US and Russia both have military forces in Syria backing opposing sides and have called for restraint on the part of Ankara's "Operation Olive Branch" to crush the YPG in the region that is near Turkey's southern border.

Turkish Foreign Minister Mevlut Cavusoglu reiterated Ankara's demand that Washington stop supporting the Kurdish force.