ISTANBUL, May 30 (Xinhua) -- The upcoming visit to the United States by Turkey's top diplomat should not be expected to settle any thorny issues between the two NATO allies other than a possible conclusion of a deal on Syria's Manbij, analysts told Xinhua.

It's not possible for the visit to yield concrete results that would meet the expectations of Ankara, said Cahit Armagan Dilek, head of the Ankara-based 21st Century Turkey Institute.

Turkish Foreign Minister Mevlut Cavusoglu is scheduled to meet with his U.S. counterpart Mike Pompeo in Washington D.C. on June 4, at a time when bilateral ties have been rather strained in recent years due mainly to U.S. military support for Kurdish militia in Syria seen by Turkey as a terror group.

For its part, Washington is highly disturbed by Ankara's close cooperation with Moscow in war-torn Syria and its bid to buy Russian-made S-400 air defense system.

Cavusoglu's visit comes after Turkish and U.S. diplomats agreed in Ankara last week on a roadmap on Manbij, where Turkey strongly opposes the presence of the U.S.-backed Kurdish militia.

The framework agreement on Manbij has boosted expectations that Cavusoglu and Pompeo would put the final seal on a deal, but the U.S. State Department said on Tuesday that no deal had been reached yet and that talks were in progress over issues of mutual concern including Syria.

Turkey sees any presence of the Kurdish militia, known as the People's Protection Units (YPG), on the western bank of the Euphrates River as a red line for its national security.

Ankara has long pushed Washington to make its Kurdish ally leave Manbij, which lies to the west of the Euphrates in northern Syria.

Dilek, a former staff officer, is not hopeful that a final agreement on Manbij would really address Ankara's security concerns.

The United States would simply try to convince Ankara that the YPG is no longer in Manbij and that the armed militants there are actually members of a local military council or the Syrian Democratic Forces (SDF), said Dilek.

The YPG, which Turkey sees as the Syrian offshoot of the outlawed Kurdistan Workers' Party, constitutes the backbone of the SDF as well as the military council controlling Manbij.

Ankara accuses Washington of trying to carve out a Kurdish state in Syria, which it considers an existential threat, along the Turkish border.

The YPG has set up three self-declared autonomous cantons in northern Syria, but the one in Afrin in the northwest was seized by Turkey in March following a two-month military campaign.

Faruk Logoglu, a former senior Turkish diplomat, is optimistic that a deal on Manbij could be finalized at the Washington meeting.

Noting that the United States needs Turkey's cooperation on Syria as well as on Iran, he said "the United States should be whispering some sweet words in Ankara's ear on the eve of the elections in Turkey."

"Cavusoglu has to return from Washington with a 'victory' in his pocket to serve as a selling point in the upcoming elections," he added. "His prize is likely to be an agreement on Manbij."

Turkey will hold snap presidential and parliamentarian elections on June 24.

If Ankara goes ahead with its plan to buy S-400 missiles, it will risk facing U.S. sanctions due to a recent U.S. Congress decision on punishing some Russian defense firms.

A U.S. Senate committee also passed a bill last week to block Turkey from purchasing Lockheed Martin's F-35 fighter jets over its detention of an U.S. priest.

Ankara has vowed to retaliate against U.S. suspended delivery of the fighter jets, the first two of which are scheduled to be handed over to Turkish pilots in the United States for training purposes by June 21.

The senate's decision was seen as a response to Ankara's move to buy S-400 defense system. The row over F-35, however, risks seriously harming ties between the two allies.

"The F-35 case can turn into a real collision course for Turkish-U.S. ties," wrote Murat Yetkin, editor-in-chief of Turkey's Hurriyet Daily News, on Monday.

Washington's apparent unwillingness to hand over a U.S.-based Turkish cleric, Fethullah Gulen, to Ankara is another point of friction in bilateral ties.

Gulen, the leader of a sort of Islamic cult whose sympathizers appeared in huge numbers in the Turkish bureaucracy including the military, is accused of masterminding a failed military coup in 2016 in Turkey.

Logoglu, who once served as Turkey's ambassador to Washington, does not expect Cavusoglu's visit to produce any concrete result other than a probable deal on Manbij.

"The daunting issues between the two allies will be relegated to the post-election period," he said.

In the view of Dilek, Ankara does not have much of a trump card to use against Washington, which, he said, will dominate the talks with Cavusoglu.

In return for encouraging much-needed capital inflow into Turkey, the U.S. would demand that Ankara should not oppose U.S. plans for the formation of a Kurdish entity in northern Syria and reduce military ties with Moscow, he said.

Turkey, in urgent need of foreign funding to keep the economy going, has been hit hard by currency depreciation amid a high inflation and unemployment.