The United States is “unwinding” Turkey from the F-35 Joint Strike Fighter program as a result of the country buying the Russian S-400 air defense missile system, Pentagon officials said.

Undersecretary of Defense for Acquisition and Sustainment Ellen M. Lord and Deputy Undersecretary of Defense for Policy David J. Trachtenberg told reporters in the Pentagon that Turkey has taken delivery of the Russian-built system. Turkey cannot have both the Russian system and the fifth-generation fighter.

Trachtenberg called the development unfortunate and said the U.S. government has worked tirelessly to avoid the necessity. “But let me be clear, the United States greatly values our strategic relationship with Turkey — that remains unchanged,” he said. “As long-standing NATO allies, our relationship is multilayered and extends well beyond the F-35 partnership. We will continue our extensive cooperation with Turkey across the entire spectrum of our relationship.”

The U.S. government has been clear over the course of this procurement that Turkey can acquire the S-400 or the F-35, but not both, he said. “Our response today is a specific response to a specific event,” he said. “It is separate and distinct from the broader range of security interests where the United States and Turkey work together against common threats. Our military-to-military relationship remains strong, and we will continue to participate with Turkey in multilateral exercises to improve readiness and interoperability.”

Trachtenberg’s remarks mirrored those of President Donald J. Trump, who said the United States values its strategic partnership with Turkey. DOD and the U.S. government worked hard to chart an alternative path that would enable Turkey to acquire air defense systems within the NATO alliance standards for interoperability and still allow Turkey to remain within the F-35 partnership, Lord said.

Turkey did not listen and bought the Russian air defense system instead of the American Patriot missile system. “The United States and other F-35 partners are aligned in the decision to suspend Turkey from the program and initiate to process to formally remove Turkey from the program,” Lord said.

The United States offered Turkey the Patriot as a missile defense system that would satisfy the country’s legitimate air defense needs. Since early 2017, when Turkey began publicly discussing its interest in the Russian-made S-400 system, all levels of the U.S. government consistently communicated to all levels of the Turkish government that the F-35 and S-400 are incompatible, Lord said.

“Turkey cannot field a Russian intelligence collection platform in proximity to where the F-35 program makes repairs and houses F-35s,” she said. “Much of the F-35 strengths lie in its stealth capabilities. So the ability to detect those capabilities would jeopardize the long-term security of the F-35 program. We seek to protect the security of the F-35.”

Turkey’s purchase of the S-400 affects the country’s interoperability with its NATO allies, she said.

Last month, then-Acting Defense Secretary Patrick M. Shanahan told Turkish Defense Minister Hulusi Akar that if his country went ahead with S-400 procurement, the country would be removed from the F-35 program. Lord said the process will be orderly and done in a respectful and deliberate manner. Turkish personnel will be reassigned away from the program by July 31. Lord said she anticipates the process of unwinding Turkey from the program will be complete by the end of March.

Turkey was going to buy 100 of the fifth-generation fighter jets and was a major player in building the system.

Lord said the F-35 international partnership is strong and resilient. “Our partnership regrets we have arrived at this moment, but I and the F-35 Joint Program Office will continue to engage fully with our F-35 partners as we continue to work to expeditiously complete the unwinding of Turkey’s participation in the partnership,” Lord said.

This will include changes to the supply base and supply chain for the aircraft system, but because of advanced planning, she anticipates minimal impact on the larger F-35 partnership. “Turkey will certainly and regrettably lose jobs and future economic opportunities from this decision,” she said. “It will no longer receive more than $9 billion in projected workshare related to the F-35 over the life of the program,” she said.

Turkey made more than 900 parts for the F-35, and that will be picked up by American suppliers to start, but will open to other nations in the months ahead.