WASHINGTON — The U.S. general nominated to lead American forces in Europe said Tuesday that if Turkey buys the Russian S-400 air defense system, it “should not get” the F-35 Joint Strike Fighter from the United States.

At his Senate Armed Services Committee nomination hearing to lead U.S. European Command, Air Force Gen. Tod Wolters called the co-location of the F-35 and the S-400 “absolutely unsustainable.”

“I concur with this committee’s belief that the S-400 and the F-35 are not compatible, and if Turkey proceeds down a path to procure and operate the S-400, they should not get the F-35,” Wolters said, adding that the Russian system “speaks a different language than NATO English.”

"We all understand that Turkey is an important ally in the region,” Wolters said. "But it’s absolutely unsustainable to support co-location of an F-35 and S-400.”

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Sen. Roger Wicker, R-Miss., said the planned S-400 buy was concerning and “not the action that one would expect from an ally,” while Sen. Thom Tillis, R-N.C., expressed his “personal concern.”

“Turkey is a partner in the supply chain in the Joint Strike Fighter, so we not only have to look at whether we can transfer those assets to Turkey, but we also have to determine what role Turkey could play in the supply chain,” Tillis said.

The remarks came a day after the U.S. stopped delivery of F-35 fighter jet parts and manuals needed to prepare for the aircraft’s planned delivery this summer.

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U.S. Defense Secretary Patrick Shanahan expressed optimism to reporters Tuesday, following a conversation with his Turkish counterpart, that Ankara would ultimately accept the Patriot air defense system that Washington has offered as an alternative.

“I am very confident in the Patriot proposal that we’ve delivered to Turkey, its availability, its pricing, and very importantly, the industrial participation that comes along with the Patriot system,” he said.

The U.S. had agreed to sell Turkey 100 of the fifth-generation aircraft made by Lockheed Martin, initially planning to deliver two aircraft to Turkey in June.

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The U.S. delivery freeze comes just days after Turkey’s foreign minister said his country was committed to the deal to buy the Russian system and was discussing delivery dates.