The Pentagon on Friday warned that should Turkey move ahead with its purchase of the Russian-made S-400 long-range air defense system, there would be “grave consequences” for Ankara.

“There would be grave consequences in terms of our military relationship with them,” US Defense Department spokesman Charles Summers told reporters at the Pentagon, The Hill reported.

Summers said that if Turkey buys the S-400, “then they would not get the F-35s,” or the Patriot system.

Turkey, a NATO ally, plans to buy Russia’s S-400 air defense system, but the US has been trying to convince Ankara to buy a Patriot air defense system instead.

Also, the US military has threatened to withhold delivery of F-35 fighter jets to Turkey if the latter goes through with the Russian purchase.

Turkish President Recep Tayyip Erdoğan, however, dismissed such threats and on Wednesday said that the decision to buy the S-400 has already been made.