President Tayyip Erdogan conveyed his priorities and expectations on Syria and other regional issues to U.S. Secretary of State Rex Tillerson in a meeting on Thursday, a Turkish presidential source said.

Erdogan and Tillerson also discussed Iraq, regional developments and the fight against terror, the source said. The more than three-hour meeting in Ankara kicked off what is widely expected to be Tillerson’s most difficult leg of a five-day regional visit.

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