Turkey has slammed an "unacceptable" U.S. resolution and expressed concern about the alliance between Ankara and Washington, saying a U.S. House of Representatives' resolution condemning Ankara's purchase of Russian air defense missile systems and urging potential sanctions was unacceptably threatening.

The resolution "Expressing Concern for the United States-Turkey Alliance" approved by the U.S. House of Representatives on Monday does not comply with the deep-rooted friendship and relations of the alliance between Turkey and the U.S., a Foreign Ministry statement said Tuesday.

"The decision ratifying unjust and unfounded allegations about Turkey's foreign policy and its judicial system is never acceptable," it added.

"It is unacceptable to make decisions that do not serve to increase mutual trust, to continue to keep the language of threats and sanctions on the agenda and to set various artificial deadlines," the ministry noted.

The ministry underlined the importance of resorting to dialogue and showing respect in order to resolve a difference of opinion between allies.

The resolution condemns Turkey's decision to acquire Russian S-400 air defense systems and calls on Ankara to cancel its procurement.

Tensions between the U.S. and Turkey have reached a fever pitch in recent months with Ankara set to begin receiving the advanced Russian surface-to-air missile system in two months. The U.S. has already suspended deliveries of parts and services related to Turkey's receipt of the multimillion-dollar jets.

Turkey decided in 2017 to purchase the S-400 system following protracted efforts to purchase air defense systems from the U.S. with no success.

However, U.S. officials have advised Turkey to buy the Patriot missile system rather than the S-400 system from Moscow, arguing it is incompatible with NATO systems. Turkey has responded that it was the U.S.' refusal to sell Patriots that led it to seek other sellers, adding Russia offered a better deal, including technology transfers. President Recep Tayyip Erdoğan said last week that the U.S. had yet to give Turkey an "offer as good as the S-400s."

The resolution urges Turkey to cancel the S-400 purchase and calls for sanctions if it accepts their delivery, which may come as soon as July.

Turkish F-35 pilots grounded at Arizona air base

On the other hand, U.S. officials said on Monday the training of Turkish pilots for F-35 fighter jets had come to a faster-than-expected halt at an air base in Arizona, as Ankara's involvement was wound down over the S-400 deal.

"The department is aware that the Turkish pilots... are not flying," said Air Force Lt. Col. Mike Andrews, a Pentagon spokesman. "Without a change in Turkish policy, we will continue to work closely with our Turkish ally on winding down their participation in the F-35 program."

The U.S. said Friday it would halt new pilot training in the F-35 fighter jet program with Turkey, one of the core partners in the F-35 program and a prospective buyer. Acting U.S. Secretary of Defense Patrick Shanahan said all Turkish pilots in the program must leave the U.S. by July 31 and training for new pilots will be suspended, according to a letter sent to Defense Minister Hulusi Akar.

The timetable would allow pilots currently training for the F-35s to complete their training and for other pilots to be reassigned to other posts, Shanahan said. The U.S. has already suspended deliveries of parts and services related to Turkey's receipt of the multi-million-dollar jets.

Four Turkish pilots are currently training at Luke Air Force Base in Arizona. Two additional Turkish pilots are at the U.S. base working as instructors.

In addition to the six Turkish officers, there are an additional 20 Turkish aircraft technicians at the base undergoing training as well, according to the U.S. military.

The disclosure of the decision on the pilots follows signs that Turkey is moving ahead with the S-400 purchase. Minister Akar said on May 22 that Turkish military personnel were receiving training in Russia to use the S-400s and that Russian personnel may come to Turkey. President Recep Tayyip Erdoğan said last Tuesday it was "out of the question" for Turkey to back out of its deal with Moscow.

Washington said S-400s would be incompatible with NATO systems and expose the F-35s to possible Russian subterfuge. But Ankara has emphasized the S-400 would not be integrated into NATO operations and would not pose a threat to the alliance.

Ankara has repeatedly said it was ready to discuss Washington's concerns. It proposed forming a joint working group to Washington to assess whether the S-400s would pose a threat to NATO; however, the U.S. has not taken any steps to form the technical team.

Turkish F-35 pilots are no longer flying at the Luke Air Force Base in Arizona as the U.S. winds down Turkey's participation in the F-35 program, the Pentagon told Reuters on Monday.

"The department is aware that the Turkish pilots ... are not flying," said Air Force Lieutenant Colonel Mike Andrews, a Pentagon spokesman.

"Without a change in Turkish policy, we will continue to work closely with our Turkish ally on winding down their participation in the F-35 program."

The Pentagon on Friday told Turkey that it was cutting off Ankara's purchase of F-35 fighter jets if the Turkish government goes ahead with plans to buy Russian-made S-400 missile defense system, ratcheting up what has been a lengthy, heated dispute between the two NATO allies.

In a sharp two-page letter, Acting Defense Secretary Patrick Shanahan said the training of Turkish pilots will end on July 31 and Turkey would not be allowed to take final possession of the four F-35 aircraft it bought. Shanahan also warned that Ankara's purchase of the Russian system could hamper America's future relationship with Turkey, which has been a critical U.S. partner and base for combat operations, including for the war in Syria.

The timetable would allow pilots currently training on the F-35 to complete their training and for other pilots to be reassigned to other posts, Shanahan said. Four Turkish pilots are currently training at Luke Air Force Base. Two additional Turkish pilots are at the U.S. base working as instructors.

In addition to the six Turkish officers, there are an additional 20 Turkish aircraft technicians at the base undergoing training as well, according to the U.S. military.