The United States will move forward with Türkiye's request to purchase F-16 fighter jets, a top official said Tuesday, as diplomacy gained pace to resolve a prolonged process that has frustrated Ankara.

Türkiye has been seeking to buy 40 new Lockheed Martin F-16s as well as nearly 80 modernization kits for its existing warplanes from the U.S., looking to revamp and refresh its aging fleet.

The Biden administration has voiced its backing for the deal potentially worth around $20 billion.

"(President Joe) Biden has been clear and unequivocal – for months he supported the transfer of F-16s," Jake Sullivan, the U.S. national security adviser, told reporters Tuesday. "He has placed no caveats or conditions on that and he intends to move forward."

Speaking to reporters ahead of a summit of NATO leaders in the Lithuanian capital Vilnius, Sullivan did not give any details on the timing but said consultations would be held with Congress to move forward with the transfer.

"So we will work with the Congress on the appropriate timing for getting them to Türkiye. But I can't speculate on the precise day it's going to happen, only that we support it getting done," he added.

It is in the interest of both the U.S. and NATO for Türkiye to receive the advanced fighter jets, Sullivan noted.

Remarks came after Türkiye late Monday withdrew its objections to Sweden joining NATO, and President Recep Tayyip Erdoğan agreed to forward to Parliament the Nordic country's bid to become a member of the military alliance.

It marked a breakthrough for the bloc's push to strengthen its defenses following Russia’s invasion of Ukraine.

Both Turkish officials and the Biden administration have rejected any suggestion that Ankara's approval of Sweden's NATO accession was being linked to the F-16 sale in the months of talks to address Türkiye's opposition.

Erdoğan and Biden are scheduled to meet Tuesday evening.

"I stand ready to work with President Erdoğan and Turkey on enhancing defense and deterrence in the Euro-Atlantic area," Biden said in a statement late Monday.

The phrasing was a nod to Biden's commitment to helping Türkiye acquire new F-16s, according to an administration official who was not authorized to comment publicly.

"I welcome a dialogue between Türkiye and the United States on the F-16 issue. However, this is not part of the compromise we reached yesterday," NATO Secretary-General Jens Stoltenberg told reporters on Tuesday.

"This is the decision of the United States. Türkiye has clarified that it does not see any connection between (the two). NATO has been very clear about what we can do to remove arms export restrictions between allies," Stoltenberg said.

Several lawmakers in U.S. Congress, most notably Senate Foreign Relations Committee Chairperson Bob Menendez, have opposed the sale and lastly tied their approval to Türkiye’s ratification of Sweden's NATO membership.

Membership of a country must be agreed upon by all 30 members of the trans-Atlantic defense alliance.

Ankara said it was strongly rejecting any conditions linked to the purchase of jets.

The U.S. government has to formally inform Congress about the arms sale. While Congress can block the process, it has not previously mustered the two-thirds majorities in both chambers to overcome a presidential veto.

In Washington, Menendez said he was in talks with the Biden administration about the hold he has on future sales of F-16 jets to Ankara.

In a brief hallway interview, Menendez, a Democrat, said while he still has concerns about Türkiye, he could make a decision within the next week about the status of that hold.

Asked whether the progress with Sweden's NATO bid might prompt him to reconsider his long-running hold on the fighter jets, Menendez said: "We're having conversations with the administration."

Asked how long it might take for him to make a decision on maintaining the hold, he responded, "Probably, if there can be one, in the next week."

Separately, U.S. Defense Secretary Lloyd Austin discussed support for Türkiye's military modernization during a call with his Turkish counterpart, according to a U.S. readout released late on Monday.

"They ... discussed the positive talks between Türkiye, Sweden and NATO Secretary-General Stoltenberg, as well as the Department of Defense's support for Türkiye's military modernization," the Pentagon said of the phone call between Austin and Defense Minister Yaşar Güler.

Ankara vowed it might consider alternatives, including Russia if the U.S. failed to follow its promise to deliver the F-16s to the Turkish Air Force.

The request for the new warplanes came instead of a refund for the $1.4 billion payment Türkiye had made for the next-generation F-35 fighter jets.

The payment was issued before Türkiye was removed from the multinational program developing the aircraft over Ankara's decision to acquire Russian-made S-400 air missile defense systems. Türkiye, which had ordered over 100 U.S. F-35s, called the move unjust and demanded reimbursement of its payment.