In a bipartisan letter sent to Defense Secretary Mark Esper on Monday, July 6, the lawmakers warned the Pentagon saying that any plans to buy F-35 fighter jet components from Turkey undercuts U.S. pressure on the country over its purchase of the Russian S-400 defense system.

The U.S. formally removed Turkey from the multinational program in 2019 over the S-400 deal, and it ended training on the jet for Turkish pilots.

The letter signed by Democrat Senators Jeanne Shaheen and Chris Van Hollen, Republican Senators James Lankford and Thom Tillis, which reminded that Under Secretary Ellen Lord had said the Department would be ending Turkey's participation "in early 2020." However, this promise of "wind-down has been neither disciplined nor punctual," the letter added.

Instead, one Pentagon official recently said that Turkish contractors would continue to make key components of the F-35 fighter jets until the end of 2022, Ahval reported.

In the letter the lawmakers also pointed to the human rights violation of the Turkish government adding that they “remain concerned about the direction Turkey is taking under the leadership of President Erdoğan.”

“From human rights violations in Syria and Iraq to arbitrary arrests of Americans in Ankara to defense cooperation with Russia, Turkey is not behaving like a responsible actor or working collaboratively with the West at the level we expect from a NATO ally,” the letter reads.

Turkey was an original F-35 partner. Its planned purchase of about 100 jets made it one of the four top foreign customers for the fighter jet, but it placed only six aircraft on contract before it was expelled from the programme last year.

The United States has said Turkey’s Russian S-400 air defense system is not compatible with NATO systems and threatens the stealth capabilities of the new fighter jets.

Turkey has disputed this and said that the S-400s will not be integrated into NATO’s defenses. Turkey had previously said it would make the Russian missile defense systems operational in April, but such a move had not yet been made.

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