Turkey will have to consider alternatives to ensure its security if the United States responds negatively to a deal for F-16 fighter jets, Defense Minister Hulusi Akar said Tuesday.

Talks are ongoing, Akar said, and a delegation from the Defense Ministry is currently in the U.S. to hold talks on Turkey’s request to buy 40 F-16s and nearly 80 modernization kits in return for the payment Ankara had allotted for the F-35 fighter jet program.

“Our contacts continue to address these and similar issues, and a delegation from our ministry is currently in the U.S.,” Akar told Parliament’s Planning and Budget Committee in the capital Ankara.

“If the U.S.’ stance is negative, Turkey will necessarily and naturally have to evaluate other alternatives in order to ensure its security in the threat environment in which it is located,” said the minister.

Turkey had paid $1.4 billion (TL 14.34 billion) for the F-35s before Washington removed it from the program in 2019 over its purchase of a Russian-made S-400 air missile defense system after its efforts to acquire U.S.-made Patriot missiles were rebuffed.

Ankara has been demanding reimbursement for its payment and said it should be used to finance some of its requests to buy F-16s and modernization kits.

Still, any military sales would have to be approved by the U.S. Congress, known for its anti-Turkey stance that has repeatedly damaged bilateral relations.

During their meeting on the sidelines of the G-20 summit in Rome earlier this month, President Recep Tayyip Erdoğan said he had asked his U.S. counterpart Joe Biden for support in getting U.S. lawmakers to back the sale.

Erdoğan said he had seen a “positive approach” from Biden on Turkey’s request. “While I saw Mr. Biden’s positive approach on this matter, another aspect of the issue is the House of Representatives and Senate,” he added.

Washington could choose a positive approach to the issue, Akar said, adding: “However, we are closely following developments (on the issue), as the process will be subject to congressional approval.”

In case the deal on F-16s fails, Ankara is still ready to consider purchasing Russian-made Su-35 and Su-57 fighter jets, officials have said.

Ankara ordered more than 100 F-35 jets made by Lockheed Martin, and its defense industry has been a prominent player in the development and manufacturing of the fighter jets.

Akar reiterated that the two NATO allies have agreed to hold a meeting in Washington in the coming period aimed at resolving the dispute over the F-35s.

The new meeting will follow the round of talks in Ankara in late October when representatives of the Turkish and U.S. defense ministries came together to discuss financial issues.

The discussions were held “for dispute resolution discussions to address remaining issues resulting from Turkey’s removal from the F-35 program, which was finalized on Sept. 23,” the Pentagon had said.

“The meeting demonstrates the commitment of Washington to conclude respectfully Turkey’s prior involvement in the F-35 program.”

The parties have agreed to meet again in early 2022, this time in the U.S., to negotiate in detail the financial issues, Akar said.

‘S-400s to be used just as S-300s’

The decades-old partnership between the NATO allies has gone through unprecedented tumult in the past five years over disagreements on many issues, including Syria and Ankara’s closer ties with Moscow.

Washington argues that the S-400 air missile systems could be used by Russia to covertly obtain classified details on the F-35 jets and that they are incompatible with NATO systems. Turkey, however, insists that the S-400 would not be integrated into NATO systems and would not pose a threat to the alliance.

The purchase of the S-400s also triggered U.S. sanctions, targeting Turkey’s Presidency of Defense Industries (SSB), its chief Ismail Demir and three other employees.

Akar said the S-400 system would be used by Turkey just as the S-300 is used in the NATO alliance, nodding to Greece’s use of the former’s predecessor missiles that are stationed on the island of Crete.

“The S-400 is a defense weapons system, and will be used in the same way as the S-300 is used in the NATO alliance,” the defense minister said.

“Our borders are protected by the most intensive measures in the history of the republic.”