Tillerson visits as Turkey says its Syria campaign over

US Secretary of State Rex Tillerson was in Ankara on Thursday for talks on the Syria conflict, just a day after Turkey announced that its military offensive was over.

Tillerson, the most senior US official to visit Turkey since President Donald Trump took office in January, is seeking to turn around recently rocky relations between the NATO allies.

He met with Prime Minister Binali Yildirim and was also due to talk to Foreign Minister Mevlut Cavusoglu.

The trip comes after Turkey announced that "Euphrates Shield", its operation in northern Syria, had ended but did not say if troops had been withdrawn from the war-torn country.

Ties between Ankara and Washington were strained during Barack Obama's administration, particularly over US cooperation with Syrian Kurdish militia fighting against the Islamic State group. Ankara views the Syrian Kurdish People's Protection Units (YPG) as a "terror group" linked to Kurdish separatists waging an insurgency inside Turkey since 1984, but Washington regards them as the best force fighting IS. Turkey has suggested it wants to join any operation to capture the IS bastion of Raqa but without involvement of Syrian Kurdish militia.

Speaking to NTV television on the eve of Tillerson's visit, Yildirim said Turkey was not yet officially informed if it would take part in a planned Raqa campaign. "The developments give an impression that the (Trump administration) is following the path of the past administration," he said, referring to the same tensions of the Obama years over the Syrian Kurdish militia role. "This issue will be told to the US Secretary of State without any buts and the United States will be asked to clarify its position."

Tillerson and Yildirim "discussed working to enhance our critical security and economic ties in the region," a State Department official said after the meeting.