Turkey gave US a 'heads up' on Syria operation

Turkey gave Washington advance warning before launching an operation against US-allied Syrian Kurdish forces around Afrin, Defence Secretary Jim Mattis said Sunday, adding that Ankara has "legitimate" security concerns.

"Turkey was candid. They warned us before they launched the aircraft they were going to do it in consultation with us, and we are working now on the way ahead through the ministry of foreign affairs," Mattis told reporters aboard his aircraft at the start of a trip to Asia.

Turkey "is the only NATO country with an active insurgency inside its borders, and Turkey has legitimate security concerns", Mattis said, referring to the Kurdistan Workers' Party (PKK), which has been engaged in a separatist struggle against Ankara since 1984.

Turkey launched its "Operation Olive Branch" offensive on Saturday, in an attempt to oust the Kurdish People's Protection Units (YPG) around the town of Afrin, a group Ankara claims is closely tied to the PKK.

Analysts believe the new conflict could put Ankara on collision course with NATO ally the US, due to Washington's alliance with the YPG during its campaign against the Islamic State group.

US jets have provided air support to the YPG - which forms the bulk of the anti-IS Syrian Democratic Forces - as they drove the miltants from swaths of Syrian territory, including its stronghold Raqqa.

This relationship and an announcement of a new US-trained border force - which will comprise mostly of Kurdish fighters - has angered Ankara.

Despite the tensions, the US on Sunday ruled out the risk of an inadvertent clash with its forces in Syria and confirmed that there were no American troops in the area the Turkish campaign was taking place.

"US officials declared that there has been no American military or American soldiers in the region," Turkish Deputy Prime Minister Bekir Bozdag told reporters in Istanbul.

In an effort to calm tensions, the US State Department said Turkey had "legitimate security concerns" and issued a call for Ankara to proceed in military operations carefully.

"We urge Turkey to exercise restraint and ensure that its military operations remain limited in scope and duration and scrupulous to avoid civilian casualties," State Department spokeswoman Heather Nauert said in a statement.

"We call on all parties to remain focused on the central goal of defeating [IS]," Nauert said.