ISTANBUL, March 31 (Xinhua) -- As the U.S. pressures Turkey to give up buying Russian-made S-400 missiles and observe sanctions on Iran while backing the Syrian Kurdish militia despite Ankara's opposition, stormy days may well be ahead in the already strained bilateral ties, analysts told Xinhua.

Things should be expected to come to a head between the two NATO allies following local elections in Turkey on Sunday, said Haldun Solmazturk, a security and foreign policy analyst.

"It's not possible to maintain so many conflicts of interest in so many areas," he argued.

According to local media, Turkish Foreign Minister Mevlut Cavusoglu will travel to the United States within days after the municipal polls over the Russian S-400 deal and Washington's latest proposal to sell Patriot missiles to Ankara in return for its backdown on the Russian air defense system.

Meanwhile, Turkish President Recep Tayyip Erdogan is scheduled to meet with his Russian counterpart Vadimir Putin in Moscow on April 8.

"I don't see it much probable for the Turkish-U.S. ties to become smooth in the near future," said Yasar Yakis, a former Turkish foreign minister.

"It should be considered a success in case relative progress could be achieved regarding some of the problems," he added.

While bilateral ties have long been going through turbulent times, Washington has revved up pressure in recent weeks as Ankara holds on to the S-400 contract.

The economic sanctions the United States reinstated on Iran last November has been another area of divergence with Ankara.

Turkey is among those granted a six-month exemption by Washington regarding oil imports from Iran, but the United States is now saying it expects Ankara to comply with the sanctions.

Solmazturk, who chairs the Incek debates at the Ankara-based 21st Century Turkey Institute, feels Turkey is now on the horns of a dilemma as a result of its badly-managed foreign policy in recent years.

The Pentagon threatened early this month that there would be "grave consequences" if Ankara would go ahead with its plan to buy the Russian missile system.

Warning that such a move would poison bilateral military ties, Pentagon spokesman Charles Summers said Ankara would not be allowed in such a case to have the fifth generation F-35 fighter jets nor the U.S. Patriot air defense missiles.

Ankara concluded the deal at the end of 2017 to get four batteries of the S-400 air defense system for 2.5 billion U.S. dollars, and the first batch is scheduled to be delivered to Ankara in July.

"Turkey got itself into a tight corner by its foreign policy and it may give up on the S-400s to get out of this," argued Solmazturk.

There have been press reports about Ankara probably passing the S-400 missiles on to another country.

However, Foreign Minister Cavusoglu underlined on Friday that there was no going back on the missile contract, denying rumors that Ankara may resell the missiles to a third country.

Some U.S. senators on Thursday introduced a bipartisan bill to block the transfer of F-35 stealth fighter jets to Turkey unless Ankara scraps the S-400 deal. The United States is also reportedly considering removing Ankara from the joint production program on F-35s.

If the S-400 deal goes through, Turkey will be the first NATO country to have acquired the sophisticated system.

On Tuesday, the United States introduced sanctions on a network comprising 25 individuals and firms which, it claimed, circumvented the U.S. sanctions on Iran. Several of the firms and persons are based in Turkey.

A day later, Sigal Mandelker, undersecretary of the U.S. Treasury for terrorism and financial intelligence, reportedly said Washington expected Ankara and all the other countries to strictly observe the sanctions against Iran.

Ankara may face U.S. sanctions in case it fails to comply with the sanctions on Iran or goes ahead with the S-400 deal.

Washington would overlook Ankara's dealings with Tehran as long as Turkey tolerates the emerging Kurdish entity in northeastern Syria, maintained Solmazturk, a former general in the Turkish military.

Washington's support for the Kurdish militia in Syria is yet another thorn in ties with Ankara.

Ankara is annoyed with Washington's continuing military support to the Kurdish militia known as the People's Protection Units (YPG), as it sees the group as a terrorist organization.

A convergence of positions regarding the YPG could emerge only if Ankara would tolerate Washington's support to the Kurdish fighters one way or another, said Yakis.

Ankara has repeatedly said it would not tolerate the YPG presence along its border, threatening to militarily intervene to eliminate the militia.

"Although an escalation of tension in ties between Ankara and Washington looks possible in the days ahead, Turkey would in the final analysis side with the U.S. due to its position on Syria," Solmazturk said, underlining that Ankara cannot strike a balance between Washington and Moscow much longer.

Turkey has a military presence on a sizable swath of land in northwestern Syria, which it captured from the Islamic State and the YPG in past operations.

"Turkey wants to be permanent in that area and the U.S. looks to be ready to accept that," said Solmazturk.

In return, Turkey would accept a Kurdish-dominated area in northeastern Syria as long as the YPG would formally remain in the background, he argued.

"If the Kurdish presence on the eastern part of the Euphrates River (in Syria) could be downsized in such a way that it is no longer perceived by Turkey as a threat, then the U.S. may close its eyes to Turkey's military presence in the western part of the Euphrates for some time," commented Yakis.

Both analysts underlined, however, that such an eventuality is sure to attract Russian and Iranian opposition, as Moscow and Tehran are supporters of the Syrian government in the war.

"A Kurdish entity in northeastern Syria can't be possibly sustained without Turkey's backing and Turkey can't maintain its presence in Syria without Washington's support," Solmazturk said.

If such a scenario implies that Turkey may annex the Syrian territory under its control, then not only Russia and Iran, but all the world would oppose it, noted Yakis.

The emergence of a Kurdish state-like entity in Syria clashes with Turkish interests, as it would be part of a greater Kurdistan project which is a threat to Turkey, Solmazturk cautioned.

The Kurdistan Workers' Party has been fighting for an autonomous, if not independent, Kurdistan in Turkey's predominantly Kurdish southeast since 1984.