President Recep Tayyip Erdogan is travelling to the US on Tuesday to take part in the White House-hosted Nuclear Security Summit and talks on the efforts to contain the Islamic State extremist militia.

Erdogan has said he will meet US President Barack Obama, but the nature and agenda of this meeting remains unclear - there is no confirmation that the White House is planning a one-to-one meeting.

On Monday, Obama's National Security Advisor Susan Rice met with Turkish Foreign Minister Mevlut Cavusoglu in Washington. Rice condemned recent attacks by Islamic State and the PKK in Turkey and reiterated the US commitment to fight the "scourge of terrorism."

She also "urged the Turkish government to uphold the universal democratic values enshrined in Turkey's constitution."

Asked Monday if relations were so bad between the two leaders that they couldn't meet face-to-face, White House spokesman Josh Earnest pointed out that the two have met numerous times over the last six months, including at the G20 summit and in Paris for the climate talks.

Saying that in terms of the fight against Islamic State, "we've got a lot of important business with the Turks to do," Earnest added that he "would anticipate that diplomacy will continue."

The two presidents have been at odds, in part over Syria but also over what US officials describe as a "drift" towards authoritarianism in Turkey.

Writing in The Atlantic magazine this month, Jeffrey Goldberg, who extensively interviewed the US president as he prepares to leave office early next year, said Obama sees Erdogan as a "failure and an authoritarian." This description was rejected in pro-government media in Turkey.

Some key issues on the two nations' agenda:

1) Islamic State: Turkey, a NATO member, was a reluctant ally of the United States in battling against Islamic State, though after many months, Erdogan eventually let the US use military bases near the border with Syria.

There are still strong disagreements over how to dislodge Islamic State from its last stretch of territory along the Turkish border. The US is allied with Kurdish fighters to push back the extremists. However, Turkey views the Kurdish militia as a terrorist group and its military has attacked them, largely due to domestic unrest with Kurdish militants on its own territory.

2) Syria: Turkey is staunchly supportive of the Syrian opposition and rebel fighters. It has been accused of backing Islamic factions with ties to extremist views. The US has been more cautious, saying Syrian President Bashar al-Assad has lost the right to rule, but has only given some weapons and training to rebels. Turkey wants a no-fly zone to support the opposition, but it cannot get Washington on board, in part due to the Russian aerial missions and defence systems in Syria.

3) Security and refugees in Europe: The US has repeatedly praised Turkey for letting more than 2 million Syrians take refuge in the country after fleeing the civil war. Recently, Ankara and Brussels reached a deal on stemming migration flows to Europe, though human rights and humanitarian aid groups have been sharply critical. The US is keen to see better security cooperation among European nations and between the European Union members and Turkey to prevent attacks like the recent tragedy in Belgium.

4) Democracy and Press Freedom: There is worry in Western circles about declining democratic standards in Turkey, including concerns over the closure of some government-critical media outlets. The US ambassador has said there is a "drift" towards authoritarianism. Last week, top Western diplomats in Turkey attended a trial of two journalists who are accused of trying to topple the government.

Erdogan, who has vowed the journalists will pay a "heavy price" for reporting on weapons shipments to Syria, has repeatedly lashed out at the foreign envoys for observing the trial, saying: "Who are you? What business do you have there? This is not your country, (this is) Turkey."

US State Department spokesman John Kirby hit an indignant tone when asked about this, saying it was a "standard diplomatic practice – to observe and report on political, judicial, and other developments in host countries. This was not only not the first time, but it darn sure won't be the last time that we observe these kinds of judicial proceedings."

5) Arrest of gold trader: Reza Zarrab, an Iranian-Turkish citizen who was at the centre of a graft scandal that rocked Turkey and its government in 2013, was arrested in the US last week on charges of violating sanctions on Iran. The corruption probe two years ago - which alleged Zarrab worked with Turkish ministers - was rejected by Erdogan as a coup attempt and was later dropped.

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