US Secretary of State Rex Tillerson says he had - what he called - a "productive and open" meeting with Turkish President Recep Tayyip Erdogan. Tillerson arrived in Ankara on Thursday. Relations between the US and Turkey have frayed due to Washington's support for the Syrian Kurdish YPG militia, which Turkey views as a terrorist group. Turkey launched an air and ground assault last month in Syria's northwest Afrin region to drive the YPG from the area near the Turkish border. Turkey has called on the US to expel the YPG from the anti-Islamic State SDF forces it is backing in Syria.