Turkey's military said on Tuesday it has killed at least 260 Syrian Kurdish fighters and "Islamic State" (IS) militants in the first four days of operations in northwest Syria's Kurdish-dominated region of Afrin.

There is no known IS presence in Afrin, which is under the control of the Kurdish People's Protection Units (YPG).

The Britain-based Syrian Observatory for Human Rights described the fighting as "very violent" to the northeast, northwest and southwest of Afrin, which lies adjacent to Turkey's southern border.

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The Observatory said 28 civilians were killed; a number vehemently denied by the Ankara government which insists it is only targeting militants. The monitoring group also said 43 Turkish-backed rebels had been killed as well as 38 Kurdish fighters, a number far lower than that provided by the Turkish military. Three Turkish soldiers have been killed since the offensive began on Saturday.

Artillery and drone strikes

The Turkish military and their Syrian rebel allies on Wednesday continued an offensive against the YPG, which the US is backing in the fight against IS, but who Ankara accuses of links to the Kurdistan Workers' Party waging a more than three decade fight in Turkey. 

The military offensive has opened up a new front in Syria's seven-year war, which could extend wider still and lead to a confrontation between Turkey and its NATO ally the US.

Turkish Foreign Minister Mevlut Cavusoglu on Tuesday said the operation could spread into the town of Manbij to the east, where some US troops are positioned alongside the SDF. He reiterated Ankara's call for Washington to stop supporting the YPG.

International reactions

So far, the international response to Turkey's incursion into Syrian territory has been muted. The United Nations Security Council called for restraint, but did not condemn the military action or call for it to end.

Read more: Turkey’s offensive in Syria: Why a muted response from the US and Russia?

Russian President Vladimir Putin spoke to his Turkish counterpart by phone on Tuesday and urged that Syria's territorial integrity and sovereignty be respected, the Kremlin said.

US Defense Secretary Jim Mattis warned that Turkey's offensive distracted from efforts to defeat IS, something Ankara rejected, saying that the extremist militant group has been effectively wiped out in Syria.

Trump to call

White House spokeswoman Sarah Sanders said Washington wanted to see Turkey "de-escalate," a move that US President Donald Trump would raise in a call with Turkish President Recep Tayyip Erdogan on Wednesday.

Russia and the US back opposing sides in Syria's civil war, with Moscow allied to Syrian President Bashar Assad's regime and Washington politically backing an alliance of opposition groups that seek to oust Assad, whose family has ruled Syria since 1971.

The US backs the Syrian Democratic Forces (SDF) militarily, led by the YPG, and whose target is primarily IS and other Islamist fundamentalist groups involved in the civil war.

Assad has denounced Turkey's offensive, along with the Kurdish-led administration of northeastern Syria, who have appealed for a mass mobilization in defense of Afrin.

The United Nations meanwhile said an estimated 5,000 people have fled the fighting since Saturday, as aid groups prepared to move in essential supplies to some 50,000 people.

mm/se (AFP, AP, dpa, Reuters)