FILE - Russian S-400 air defense missile systems drive during the Victory Day military parade marking 71 years after the victory in WWII in Red Square in Moscow, Russia, May 9, 2016.
FILE - Russian S-400 air defense missile systems drive during the Victory Day military parade marking 71 years after the victory in WWII in Red Square in Moscow, Russia, May 9, 2016.

ISTANBUL, TURKEY - Washington is ratcheting up pressure on Ankara over its decision to buy a Russian missile system, which was confirmed last month by Turkish President Recep Tayyip Erdogan. Senior U.S. diplomats held talks this week in the Turkish capital to lobby against the sale as Washington warns of "grave consequences."

Deputy Assistant Secretary Matthew Palmer met Wednesday with senior Turkish officials in the latest diplomatic effort to block Ankara's procurement of Russia's S-400 missile system.

However Erdogan reiterated his commitment to buy the Russian system. In a television interview Wednesday, he indicated interest in expanding the purchase to Russia’s more advanced S-500 system.

"I would hope that they [Ankara] reconsider this one decision on S-400," U.S. General Curtis Scaparrotti told the Senate Armed Services Committee on Tuesday.

FILE - U.S. Army General Curtis Scaparrotti, Comma
FILE - U.S. Army General Curtis Scaparrotti, Commander of the U.S. European Command, testifies on Capitol Hill in Washington, March 8, 2018.

Scaparrotti warned that the sale poses a threat to American systems used by Turkey, "it's a problem for all of our aircraft, but specifically the F-35, I believe."

The F-35 is America's newest and most technologically advanced plane. Turkey is a co-producer of the aircraft and is due to buy a 100, of which the first two are due to be delivered later this year.

Washington fears the sophisticated radar of the S-400 system could compromise the F-35 technology, which was developed to elude Russian-made systems.

Turkey's purchase of the F-35 is now under threat.

FILE - The F-35 Lightning II hovers in front of cr
FILE - The F-35 Lightning II hovers in front of crowds during its first solo appearance at the Farnborough Air Show in the United Kingdom, July 12, 2016.

"Turkey's acquisition of the Russian S-400 air-defense system will have grave consequences for the U.S. defense relationship with Turkey," U.S. Pentagon spokesman Nick Pahon said Monday in a statement.

Ankara insists the S-400 offers the best value for its needs and poses no threat to NATO systems. Washington is offering an alternative to the S-400, its more expensive Patriot missile system, but negotiations with Ankara remain stalled over pricing and technology-transfer issues.

Analysts warn the consequences for Ankara, however, could be far-reaching. "If this purchase would go through, even beyond these military aspects, the escalation in Turkish-U.S. tensions would be significant in terms of affecting Turkey's political risk, for the economy," said Sinan Ulgen head of the Istanbul based think tank Edam.

Warning to Turkey

The decision by U.S. President Donald Trump on Monday to include Turkey along with India in ending a preferential trade agreement is widely interpreted as a warning to Ankara. While the move affects just one percent of Turkey's total exports, the Turkish currency fell sharply on the news.

"It is clear that the general tendency in Washington, D.C., is to punish Turkey for perceived misconduct, which remains a significant threat to the Turkish economy," said Atilla Yesilada of Global Securities.

Turkey's economy is still reeling from a 2018 spat with Washington. Last year, the Turkish currency collapsed after Trump hit Ankara with sanctions over the detention by Turkey of American pastor Andrew Brunson, who has since been released. Although the sanctions lasted only a few weeks, Turkey's economy now faces a recession.

President Donald Trump prays with American Pastor
FILE - President Donald Trump prays with American Pastor Andrew Brunson in the Oval Office of the White House, Oct. 13, 2018, in Washington. Brunson was detained for nearly two years in Turkey.

Washington has various means to inflict further pain on the Turkish economy. U.S. Treasury authorities are still considering imposing a potential multibillion-dollar fine on Turkish State lender Halk Bank after the conviction of one of its senior employees by a New York court for violating the United States' Iranian sanctions.

Ankara is not expected to make any concessions, though, before crucial local elections on March 31. Analysts say taking a hardline against Washington plays well among Erdogan's supporters.

Upcoming meeting

Erdogan said last month that Trump had agreed to meet in April. Ankara officials claim the two presidents maintain a strong working relationship, and they blame current bilateral tensions on ministers and advisers around the U.S. president.

Analysts point out that Erdogan probably will be buoyed by Trump's silence on the controversy of the S-400 deal. "Ankara only cares about what Trump says for Ankara as only Trump is its interlocutor," said former senior Turkish diplomat Aydin Selcen, who served in Washington.

Erdogan is widely seen as being unlikely to give up on the Russian missile purchase before meeting Trump. "This could be seen as essentially a negotiating position," Ulgen said.

But the S-400 purchase also is a powerful symbol of Ankara's deepening relationship with Moscow. The two countries increasingly are cooperating in efforts to end the Syrian civil war, despite backing rival sides in the conflict.

FILE - Turkey's President Recep Tayyip Erdogan, ri
FILE - Turkey's President Recep Tayyip Erdogan, right, shakes hands with Russia's President Vladimir Putin following their joint news statement after their meeting at the Presidential Palace in Ankara, Turkey, Dec. 11, 2017.

The current thaw followed painful economic sanctions by Moscow on Ankara after a Turkish jet downed a Russian bomber attacking Syrian rebel forces. Analysts suggest Erdogan will be wary of again provoking Russia. Before the downing of the Russian jet, Turks enjoyed visa-free travel.

"Turkey once betrayed the Russians, shooting down their fighter, and the Russians have not forgotten this," said international relations professor Huseyin Bagci of Ankara's Middle East Technical University. "If Russia really trusted Turkey, they would lift their visa requirement, but they still have it. It means Turkey doesn't deserve the Russians' trust."

Observers warn the S-400 missile sale poses Ankara with a diplomatic conundrum: how to avoid drawing the ire of either Washington or Moscow.