Türkiye is moving swiftly toward the final step on Sweden's NATO membership as it is expected to send the final instrument of its ratification to Washington within days in a move Ankara hopes will clear the way to its purchase of U.S. F-16 fighter jets.

A source familiar with the issue said the document could be deposited as early as Friday, marking the last step in a process that began in 2022.

Swedish Prime Minister Ulf Kristersson welcomed Türkiye's move, saying on X, formerly known as Twitter: "With this, a key milestone has been reached in Sweden’s path toward NATO membership."

Türkiye’s Parliament passed the motion in a vote held Tuesday after more than a year-and-a-half of delays that frustrated other allies who argued Sweden's entry would strengthen NATO.

On Thursday, Parliament's endorsement of Sweden's membership and a decree President Recep Tayyip Erdoğan signed off approving its accession protocol were published in Türkiye's Official Gazette, concluding the ratification process in the country.

As per formal NATO rules, the final document in the process – the instrument of ratification – needs to be deposited in the U.S. State Department archives in Washington.

Türkiye's backing, long seen as the main obstacle in securing Sweden's accession into the Western military alliance, leaves Hungary as the only ally in the military alliance yet to ratify the Swedish bid.

Sweden, along with Finland, abandoned its traditional position of military nonalignment to seek protection under NATO’s security umbrella, following Russia’s invasion of Ukraine in February 2022. Finland in April became NATO’s 31st member after Türkiye’s Parliament ratified the Nordic country’s bid.

But Türkiye held out on approving Sweden's bid, accusing the country of being too lenient toward terrorist groups like the PKK, which has led a bloody insurgency against the Turkish state for over four decades, and the Gülenist Terror Group (FETÖ), which was behind a defeated coup attempt in 2016. Ankara sought a series of concessions from Stockholm, including moves to counter the members and supporters of the said groups.

Türkiye also had been angered by a series of demonstrations by supporters of the PKK in Sweden as well as Quran-burning protests that roiled Muslim countries.

Both Erdoğan and members of the U.S. Congress had previously linked Ankara's final approval of Sweden to the $20 billion (TL 605 billion) sale of Lockheed Martin F-16s and modernization kits to Türkiye.

Erdoğan has also called on Canada and other NATO allies to lift arms embargoes imposed on Türkiye.

Shortly after the Turkish Parliament's vote, U.S. President Joe Biden sent a letter to leaders of key Capitol Hill committees to inform them of his intention to begin the formal notification process for the F-16 sale once Ankara completes Sweden's NATO accession process.

Secretary of State Antony Blinken welcomed Erdoğan’s signature of the ratification.

"We look forward to receiving the instruments (of ratification) in Washington and welcoming Sweden as NATO's 32nd Ally. Sweden and the Alliance are stronger together," he wrote on X.

The U.S. ambassador to Türkiye told Reuters on Thursday that he expected Washington to take rapid steps toward U.S. Congress endorsement of the sale, with the State Department sending the formal notification to Congress immediately.

During the vote on Tuesday, Erdoğan’s ruling Justice and Development Party (AK Party) said Sweden's tougher stance on PKK terrorists was key to winning approval.

Senior ruling party legislator Fuat Oktay said that Sweden had amended its counterterrorism laws, curbed the PKK’s financial activities, convicted a terrorism suspect and extradited another, and lifted restrictions on arms sales to Türkiye.

With Türkiye finalizing its approval, all eyes have turned to Hungary.

A vote on the protocols for Sweden’s NATO accession hasn’t yet appeared on the Hungarian Parliament’s agenda, and barring a surprise emergency session, the matter is unlikely to go before lawmakers until at least late February.

Hungarian Prime Minister Viktor Orban says his government is in favor of bringing Sweden into NATO, though he has also suggested that members of his governing Fidesz party remain unconvinced because of some Swedish politicians' statements about the state of Hungary's democracy.

The Swedish and Hungarian prime ministers will meet next week at the European Council meeting in Brussels, but Kristersson said Sweden would not make any new promises on NATO.

"No demands that are related to NATO membership - that's not on the table," Kristersson told Sweden's TV4.

However, he said the two countries had much to discuss, including cooperation inside NATO, Hungary's upcoming EU presidency, support for Ukraine and how to get the widest synergies from their airforces sharing the same fighter jet program - Sweden's JAS Gripen.