US President Joe Biden underlined the strength of NATO as Finland and Sweden join the alliance, amid altered security architecture in the West following Russia's continued war against Ukraine.
"Our alliance is closer than ever. It is more united than ever. And when Finland and Sweden bring the number of allies the 32 will be stronger than ever stronger than that," Biden said on Tuesday as the US ratified instruments for the Nordic countries' accession.
Last week, large majorities of Democrats and Republicans voted in favour of enlarging NATO, reports dpa news agency.
Washington said the US is the 23rd of the 30 NATO member states to approve the accession.
"In a moment when Putin's Russia has shattered peace and security in Europe, when autocrats are challenging the very foundations of a rule based order, the strength of the Transatlantic Alliance, and America's commitment to NATO is more important than has ever been," Biden said.
He urged the other allies to complete their own ratification processes as soon as possible.
Finland and Sweden both put aside decades of neutrality to join NATO following Moscow's invasion of its neighbour in February.
Before the accession protocols can enter into force, they must be ratified by the 30 NATO member states.
It remains unclear whether Turkey will do so, as the only member to block the accession process.