The relationship between key NATO allies the United State and Turkey continues to unravel, and the transfer of next-generation fighter jets to Turkish soil now looks like it will be one casualty.

According to the Pentagon’s top spokesperson, If Ankara moves forward with a deal to buy a Russian anti-aircraft missile system, Turkey will be blocked from taking home the stealth F-35 aircraft – which they have already received in the United States.

In addition, acting press secretary Charlie Summers said that they will forfeit any potential purchase of Patriot missiles as well, Defense News reported.

His comments come after Turkish President Tayyip Erdogan dismissed US concerns earlier in the week, saying that the ink on the contract with Russia was already dry and that Ankara will consider purchases of future Russian systems.

“We concluded the S-400 issue, signed a deal with the Russians and will start co-production,” he said. “Later, we may work with S-500s,” he added.

On Friday morning, Turkish defense chief Hulusi Akar said that he was told by Pentagon officials that – under these circumstances – there would be no way to pass the sale of F-35s to Turkey.

“Our peers say it is impossible to pass the sale of the F-35 aircraft in Congress, but we are working on a solution,” he said, according to Turkey’s Anadolu Agency. “We have to protect and cover our 82 million citizens. S-400 systems will begin to be established in October. The Air Force continues to work where they’ll be stationed.”

The tone from the Pentagon is a shift from efforts by former Defense Secretary James Mattis to convince Congress to keep Turkey in the program. At risk for the US is the delivery of the aircraft to other allies in the consortium, which could face significant delays if Turkey were cut out, due to its role in production.

When asked in a hearing before the Senate earlier this week whether Turkey’s role in producing components poses a problem, the top US commander in Europe suggested it would be a bigger loss for Turkey than for the United States.

“I would just underscore the fact that this is a… huge decision for Turkey,” General Curtis Scaparrotti, head of US European Command, told the Senate Armed Services Committee. “It connects in many different ways – to the employment and the integration that they have within the [F-35] system itself – but also to FMS (foreign military sales) and other systems we sell to Turkey as well.”