Pentagon spokesman Charles Summers told reporters Turkey's decision to accept the Russian defense system "would mean that they would not have access to the Patriots and the F-35s.”

"If Turkey takes the S400s there will be grave consequences in terms of our military relationship with them and with the Patriots and the F-35s," Summers said.

He did not provide any additional consequences, Anadolu reported.

Earlier this week, Gen. Curtis Scaparrotti told a Senate committee he hopes Turkey would reconsider its decision to purchase the S-400 system.

Scaparrotti, who also serves as NATO's top commander, pointed to several problems the Russian system poses, including lack of interoperability with NATO systems and said the S-400 is "a problem to all of our aircraft, but specifically the F-35, I believe."

After protracted efforts to purchase air defense systems from the U.S. with no success, Ankara decided in 2017 to buy Russian S-400 air defense systems.

The move was criticized by the Pentagon, which warned that purchasing the S-400 would hurt Turkish-U.S. relations and Turkey's role in NATO.

Washington has cautioned the S-400 system might covertly obtain critical information on the advanced fighter jets, including their detection range, which could then be relayed to Russia.

But Turkish officials said Ankara would not go back on its agreement with Russia, even if it were to also buy the Patriot system.

Turkish Defense Minister Hulusi Akar stressed Ankara purchasing the S-400s from Russia is "not a choice but a necessity."

Turkey's Foreign Minister Mevlut Cavusoglu said last week Ankara and Washington have begun negotiating the potential purchase of Patriot missile defense systems from the U.S.

The State Department approved in December a possible $3.5 billion sale of Patriot systems to Turkey that includes advanced radar systems, control centers, launching systems and guided missiles.

Ankara is planning to purchase 100 F-35 fighter jets from the U.S. pending congressional approval, and its pilots are currently training on the weapons platform at Luke Air Force Base in Arizona.

Turkish firms also supply the F-35 program with key components, including airframe structures and assemblies, and the center fuselages.

On March 6, Turkish President Recep Tayyip Erdogan said Ankara finalized a deal on purchasing the S-400 missile system from Russia, and that in the future "we may work with S-500s," the next-generation Russian missile system.

Akar added starting this October, the S-400 systems will be installed in Turkey, adding that the Turkish Air Force is working on where to deploy the missiles.

Reporter’s code: 50101