By Ece Toksabay, Ellen Francis and Tuvan Gumrukcu

ANKARA/BEIRUT (Reuters) – The U.S.-backed Syrian Democratic Forces (SDF) rejected a Turkish army statement that Islamic State was present in the Afrin region of northwestern Syria, where Ankara launched an offensive four days ago which has raised international concern.

The Turkish military said late on Tuesday it had killed at least 260 Syrian Kurdish fighters and Islamic State militants in its offensive into the Kurdish-dominated Afrin region of northwest Syria.

Turkey’s air and ground operation has opened a new front in Syria’s multi-sided civil war and could threaten U.S. plans to stabilize and rebuild a large area of northeast Syria – beyond President Bashar al-Assad’s control – where Washington helped the SDF to drive out Islamic State militants.

“The whole world knows Daesh (Islamic State) is not present in Afrin,” Redur Xelil, a senior SDF official, told Reuters. He said the Turkish military had greatly exaggerated SDF casualties, though he declined to say how many had been killed.

Turkey sees the YPG – the most powerful faction within the SDF – as an extension of a Kurdish group that has waged a decades-long insurgency in southeastern Turkey. It has long said it will not allow the Kurdish fighters to control a strip of Syrian territory on its southern border.

U.S. President Donald Trump plans to raise concerns with Turkish President Tayyip Erdogan in a phone call expected on Wednesday about Ankara’s offensive against Kurdish YPG fighters in Afrin, a senior U.S. official said.

French President Emmanuel Macron also voiced disquiet, a few hours after Turkey’s foreign minister said it wanted to avoid any clash with U.S., Russian or Syrian government forces during its offensive but would do whatever necessary for its security.

The United States and Russia both have military forces in Syria backing opposing sides and have called for Turkish restraint in its “Operation Olive Branch”, meant to crush the YPG in the Afrin region near Turkey’s southern border.

A senior Trump administration official, who briefed reporters on condition of anonymity, said Ankara had sent “conflicting signals” about the scope of the offensive.

“We’re going to have to see how this develops on the ground. But our message has been unified. We would appreciate it and we would urge them to limit the incursion as much as possible.”

Erdogan told Macron on Tuesday that Turkey was taking all measures to prevent civilian casualties in the Afrin operation, sources at the presidential palace said. The two leaders agreed to stay in close contact on the issue.

The Kremlin said President Vladimir Putin had also discussed Turkey’s operation with Erdogan by phone and that Syria’s territorial integrity and sovereignty had to be respected.

A Kremlin statement said both men stressed the importance of continuing their two countries’ joint work to try to find a peaceful resolution to Syria’s crisis. Russia has been Assad’s most powerful ally against rebels and militants in Syria.

Turkish Foreign Minister Mevlut Cavusoglu reiterated Ankara’s demand that Washington stop supporting the YPG.

Ankara has said the operation will be swift, but Erdogan’s spokesman signaled an open-ended cross-border campaign, saying it would end only when some 3.5 million Syrian refugees now living in Turkey could safely return home.

The United States hopes to use the YPG’s control in northern Syria to give it the diplomatic muscle it needs to revive U.N.-led talks in Geneva on a deal that would end Syria’s civil war.

NEAR BREAKING POINT

Ankara has been infuriated by the U.S. support for the YPG, which is one of several issues that have brought ties between Washington and its Muslim NATO ally close to breaking point.

“The future of our relations depends on the step the United States will take next,” Cavusoglu said.

Turkey’s military, the second largest in NATO, has conducted air strikes and artillery barrages against targets in Afrin, and its soldiers and allied Syrian rebels tried to thrust into the Kurdish-held district from west, north and eastern flanks.

With heavy cloud hindering air support in the last 24 hours, advances have been limited and Kurdish militia have retaken some territory. Turkish troops and the Syrian fighters have been trying to take the summit of Bursaya Hill, overlooking the eastern approach to Afrin town.

The Syrian Observatory for Human Rights, a Britain-based war monitor, said 23 civilians had been killed in Turkish shelling and air strikes, and thousands were fleeing the fighting.

However, Syrian government forces were preventing people from crossing government-held checkpoints to reach the Kurdish-held districts of nearby Aleppo city, it said.

Xelil, the SDF official, said the SDF had killed tens of Turkish forces and allied Free Syrian Army fighters, but said he did not have a precise figure.

YPG THREAT

U.S. Defense Secretary Jim Mattis said Turkey’s offensive was distracting from efforts to defeat Islamic State.

Ankara says the jihadist group is largely finished in Syria and that the greater threat comes from the YPG.

Erdogan has said Turkey aims to destroy YPG control not just in the Afrin enclave but also in the mainly Arab town of Manbij to the east.

“Terrorists in Manbij are constantly firing provocation shots. If the United States doesn’t stop this, we will stop it,” Cavusoglu was reported as saying on Tuesday.

“Our goal is not to clash with Russians, the Syrian regime or the United States, it is to battle the terrorist organization,” broadcaster Haberturk quoted him as saying.

He tweeted that a lieutenant had become the second Turkish soldier to be killed in the operation. The Observatory said 43 rebels fighting alongside the Turks had also been killed, as well as 38 on the Kurdish side.

Later on Tuesday, Cavusoglu discussed the crisis with U.S. Secretary of State Rex Tillerson during a conference in Paris.

Erdogan’s spokesman, Ibrahim Kalin, said the military operations would continue until Syrian refugees in Turkey “return home safely and the separatist terror organization has been cleansed from the region”.

The Kurdish-led administration of northeastern Syria appealed for a mass mobilization in defense of Afrin. “We call on all our people to defend Afrin and its pride, and contribute in all the related activities,” it said, without elaborating.

A U.N. report, citing local sources, said about 5,000 people in the Afrin district had been displaced as of Monday but that some of the most vulnerable had been unable to flee. It said the United Nations was ready to provide aid to 50,000 in Afrin.

(Additional reporting by Tuvan Gumrukcu in Ankara, Tom Perry in Beirut, Suleiman al-Khalidi in Amman, Steve Holland in Washington and Michel Rose in Paris; writing by Dominic Evans; editing by Mark Heinrich, Cynthia Osterman and Nick Tattersall)