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ANKARA, Turkey — America’s top diplomat Rex Tillerson was in Turkey on Thursday for what promised to be tough talks with a key but complicated partner in the U.S.-led campaign to defeat ISIS.

NBC News looks at the main challenges the secretary of state faces as he sits down with Turkish leaders in the country's capital of Ankara — a place where East meets West.

Opposition to Kurdish role

Following up on the 66-nation counter-ISIS summit held in Washington last week, Tillerson was set to talk to Turkish President Recep Tayyip Erdogan about his long-held opposition to the YPG — a Kurdish militia and important U.S. ally in Syria.

The YPG have been on the front lines in the fight against ISIS and will be crucial in the coalition's upcoming campaign to retake the city of Raqqa, the extremists' de facto capital. Discussions will be difficult for Tillerson, however, because Erdogan sees the YPG as terrorists and equivalent to PKK Kurdish separatists, who are blamed for attacks inside Turkey.

Secretary of State Rex Tillerson, left, shakes hands with Turkish President Recep Tayyip Erdogan during their meeting in Ankara on Thursday. Turkish President Press Office via EPA

Tillerson and Turkish officials will also discuss "interim zones of stability," a strategy to create protected areas in Syria that help refugees to return home. Tillerson announced the concept to the anti-ISIS coalition last week but details of how these areas would be protected have not been released.

A senior State Department official who briefed reporters said that ceasefires would be important to the success of this strategy and Turkey has been working with Russia and Iran to put these in place.

Several proposals for safe zones or no-fly zones aimed at protecting Syrian civilians have been considered since the start of the Syrian civil war but not put in force. Implementing them would require extensive resources and risk inflaming the conflict. It isn't clear how President Donald Trump's administration is planning on addressing these issues.

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Turkish power politics

Politician tensions in Turkey will complicate Tillerson's meetings further with Erdogan’s government in the midst of a nationwide crackdown that started after an attempted coup last summer. A referendum vote next month could grant the president sweeping new powers under an altered constitution.

A senior State Department official said Tillerson is "acutely aware" of the delicate situation he faces faces in Turkey. Although he does not plan to meet with opposition leaders or dissidents during Thursday's visit, officials say he will not hesitate to address human rights abuses as the State Department has done in the past.

Related: Turkey Post-Coup Purge: 15,000 More Government Employees Fired

The State Department also highlighted American concerns just 24 hours before Tillerson’s trip with a travel warning pointing to an increase in terrorist threats and abuse by the Turkish state. The advice cautioned U.S. citizens to "carefully consider the need to travel to Turkey at this time."

The advisory also warned that the expanded powers of the Turkish government under an extended state of emergency have been used by the government to "restrict internet access as well as media content," and "U.S. citizens have been deported and/or detained and held without access to lawyers or family members.”

Fate of cleric hangs in balance

The State Department’s warning cautioned that "an increase in anti-American rhetoric has the potential to inspire independent actors to carry out acts of violence against U.S. citizens."

That anti-American rhetoric stemming from the Turkish government points to yet another challenge facing Tillerson on his one day trip to Turkey — the fate of cleric Fetullah Gulen, who lives in a religious compound in the Poconos, Pennsylvania.

Supporters of the Vatan Partisi, or Patriotic Party, shout slogans and hold signs condemning "American imperialism" as they protest the visit to Turkey by Secretary of State Rex Tillerson outside the U.S. consulate in Istanbul on Thursday. Ozan Kose / AFP - Getty Images

The Turkish government has repeatedly demanded the United States extradite Gulen, who they hold responsible for last July's coup attempt. Gulen strongly denies the charges and is protected from extradition without a proper investigation under U.S. law.

Another State Department official who briefed reporters said the extradition was a subject for the Justice Department but added that Tillerson would be prepared to address it if asked.

Related: Nervous NATO's Biggest Concern? The White House

Former CIA Director Jim Woolsey told NBC News on Monday that a plan to get around extradition laws by kidnapping Gulen was discussed at a meeting he attended with top Turkish officials and convened by then-candidate Donald Trump’s national security campaign adviser Michael Flynn.

NBC News was not able to confirm Woolsey’s account and a Flynn spokesman told The Associated Press the claims are "false" and that "no such discussion occurred."

Flynn, who was fired in February after it emerged that he had misled Vice President Mike Pence about his communications with the Russian ambassador, later disclosed that he was a paid lobbyist for Turkey at the time.

After Turkey, Tillerson heads to NATO headquarters in Brussels, Belgium, where State Department officials say the fight to defeat ISIS will remain at the top of the agenda.