ANKARA, Turkey — The Trump administration and Turkey appeared no closer Thursday to resolving a dispute over the Kurds’ role in defeating the Islamic State group in Syria, as US Secretary of State Rex Tillerson visited America’s often nettlesome NATO ally for the first time.

Although the disagreement centers on tactics for a long-planned assault on ISIS’s self-declared capital of Raqqa, Turkey’s long-term security is also at stake. For decades, Turkey has battled Kurdish militants inside its own borders. So Turkey is loath to tolerate the US partnering against ISIS with Syrian Kurdish fighters instead of Turkey’s own military and affiliated Syrian forces.

‘‘Let me be very frank: These are not easy decisions,’’ Tillerson said after meeting President Recep Tayyip Erdogan and other top Turkish officials.

The dispute has deepened a divide between two allies that have agreed on little in recent years. The Obama administration long complained about Turkey’s inability to seal its frontier to prevent extremist recruits from reaching Middle East battlefields, and the frustration has carried over under President Trump as the United States looks to deal ISIS death blows in Iraq and Syria.

Turkey accuses the Kurdish fighters known as the YPG of being an extension of a Kurdish insurgent force within Turkey that the United States also considers a terrorist organization.

Turkey says the United States is backing one terror group to fight another, to the detriment of Turkish security, after spending years allowing Syria’s civil war to spiral out of control.

But the United States considers Syrian Kurdish fighters the most effective force at fighting ISIS and critical to liberating Raqqa.

And despite Trump and Erdogan’s talk of improving US-Turkish ties, the countries continue to clash over many matters, including the fate of a Pennsylvania-based cleric that Turkey blames for a failed coup attempt in July.

Washington hasn’t announced which fighters will lead the Raqqa operation, though signs point to a prominent role for the Kurdish-led group, which also includes Arab fighters. The United States airlifted hundreds of so-called Syrian Democratic Forces behind enemy lines in Syria last week in what officials described as a key step toward Raqqa.

Tillerson said he and Turkish Foreign Minister Mevlut Cavusoglu explored several ideas for the Raqqa operation, signaling no agreement. The countries will discuss the matter further, he said, insisting each is committed to defeating ISIS.

Yet Cavusoglu struck a far less sanguine tone, declaring that US support for the Kurds already had damaged ties. ‘‘It has negatively affected the Turkish people’s sentiments toward the United States,’’ he said in Turkish.

Turkey had been backing its own proxy fighters in Syria, drawing US complaints about a lack of coordination with other coalition members.

Washington also accuses Turkey of being more focused on preventing Syrian Kurds from forming an autonomous region in northern Syria, along Turkey’s border, than accelerating the fight against ISIS.

Turkish Prime Minister Binali Yildirim announced the operation’s end this week after Turkish troops and allied rebels secured border territory. ‘‘Life is back to normal. Everything is under control,’’ he said on Turkey’s NTV news channel.

The Turkish-backed Syrian fighters are now restructuring themselves ahead of another battle. Discussions are occurring about keeping the forces under Turkey’s direction or transferring them to US leadership, Colonel Ahmad Othman told The Associated Press.

‘‘This doesn’t mean operations are over,’’ Othman said.

Both countries have shifted priorities after spending years calling for the ouster of Syrian President Bashar Assad. Trump has shown a clear preference for dealing with ISIS first, while Erdogan has repaired ties with key Assad-backer Russia.

Also hanging over Tillerson’s trip was Turkey’s demand that the United States extradite Fethullah Gulen, the cleric Turkey says instigated last year’s failed coup. He denies involvement. The United States has said Turkey hasn’t provided sufficient evidence.

Cavusoglu insisted Turkey had plenty of evidence and said Attorney General Jeff Sessions committed to ‘‘evaluate the documents meticulously.’’ At a minimum, he said, Turkey wants the United States to arrest Gulen while it weighs extradition.

‘‘We are expecting concrete steps,’’ he said. ‘‘We need to take mutual steps to put relations with the United States back on track.’’