US Secretary of State Rex Tillerson completed his first official trip to Turkey since taking office, apparently without resolving any of the fundamental differences that have sunk relations between the two NATO allies to their weakest since the 2003 occupation of Iraq.

There are multiple sources of friction: Washington has so far refused to extradite Fethullah Gulen, the Muslim cleric Ankara accuses of engineering the failed July 15 coup. On Monday, a senior executive of one of Turkey’s largest state-owned banks was arrested in the United States on charges of conspiring to evade trade sanctions on Iran. Halkbank executive Mehmet Hakan Atilla is accused of plotting with Reza Zarrab, an Iranian-Turkish gold trader with close ties to the Turkish government who was arrested in Miami a year ago for similar offenses. Turkey called the arrests politically motivated.

But nothing incenses Turkey as much as the US support for Syria’s Kurds.

In meetings with Turkish President Recep Tayyip Erdogan, Prime Minister Binali Yildirim and Foreign Minister Mevlut Cavusoglu, Tillerson is believed to have confirmed the administration’s decision to press ahead with plans to capture Raqqa, the Islamic State’s last remaining stronghold in Syria, with the help of the Kurdish-dominated Syrian Democratic Forces (SDF). Tillerson’s meeting with Erdogan lasted over two hours.