All 30 NATO allies must give their consent for the accession of Sweden and Finland into the military alliance.
More than two-thirds of NATO allies have already ratified the membership of Finland and Sweden, less than a month after the two Scandinavian countries concluded accession talks.
Twenty-three of NATO's 30 allies have by now given their necessary formal stamp of approval for the accession of Finland and Sweden into the military alliance, with the US and Italy becoming the latest to do so on Wednesday.
The US Senate approved the move with a 95-1 vote while the Italian parliament did so with 202 votes in favour, 13 against and one abstention.
US President Joe Biden welcomed the "historic vote" in a statement, saying it "sends an important signal of the sustained, bipartisan US commitment to NATO, and to ensuring our Alliance is prepared to meet the challenges of today and tomorrow".
"Finland and Sweden joining the Alliance will further strengthen NATO's collective security and deepen the transatlantic partnership," he also said, adding: "I look forward to signing the accession protocols and welcoming Sweden and Finland, two strong democracies with highly capable militaries, into the greatest defensive alliance in history."
He then officially signed the Instruments of Ratification on 9 August in the presence of the Swedish and Finnish ambassadors to the US.
The votes in the US Congress and Italian parliament came just a day after French lawmakers also backed the two countries' accession to NATO in a 209-46 ballot.
Finland, which borders Russia, and Sweden were traditionally against joining the military alliance but public opinion in both countries swiftly changed after Moscow launched its war against Ukraine on 24 February. Less than two months later, they simultaneously handed in their official letters of application.
But Turkey blocked their accession for weeks, accusing them of sheltering activists from the Kurdistan Worker's Party (PKK) which it, the EU and NATO, consider a terrorist group.
Ankara lifted its veto on 29 June, hours before the beginning of a key NATO summit in Madrid, after the three countries struck a memorandum in which they stated their "unwavering solidarity and cooperation in the fight against terrorism, in all its forms and manifestations, which constitutes a direct threat to the national security of Allies as well as the international peace and security."
Finland and Sweden also confirmed that they consider the PKK a proscribed terrorist organisation, committed to preventing its activities and to step up cooperation to prevent its activities. They also committed to address Turkey's pending deportation or extradition request of suspected PKK activists.
Six days later, on 5 July, the accession protocols were signed and Jens Stoltenberg, NATO's Secretary General, pledged that their accession would "be the fastest in history."
"I'm very careful predicting or promising anything [about] parliaments. But last time, it took roughly a year and many allies have expressed that they can try to do it faster this time," Stoltenberg told Euronews at the time.
"So hopefully we will most likely speak about months," he added.
Lawmakers in Canada, Denmark, Iceland, Norway, Estonia, the UK, Albania and Germany endorsed their accession that very week.
A month later, Turkey is one of just seven allies with the Czech Republic, Greece, Hungary, Portugal, Slovakia and Spain whose lawmakers have not yet been asked to vote on Finland and Sweden's accession to NATO.