ANKARA (Reuters) - U.S. Secretary of State Rex Tillerson and Turkish President Tayyip Erdogan on Thursday had a “productive, open conversation” about a mutually beneficial way to improve U.S.-Turkey relations, a State Department spokesman travelling with Tillerson said.

Tillerson met with Erdogan for more than three hours in Ankara, as part of what was widely expected to be the most difficult leg of a five-day regional visit.

Relations between the NATO partners have been strained over a number of issues, particularly Washington’s support for the Syrian Kurdish YPG militia, which Ankara calls terrorists.