"The United States will work with Finland and Sweden to remain vigilant against any threats to our shared security, and to deter and confront aggression or the threat of aggression" while their bid is considered, Biden said in a statement.

Biden, who will welcome Finnish President Sauli Niinisto and Swedish Prime Minister Magdalena Andersson to the White House on Thursday, said he was looking "forward to working with the US Congress and our NATO allies to quickly bring Finland and Sweden into the strongest defensive alliance in history."

"I warmly welcome and strongly support the historic applications," Biden said.

The two countries formally handed in their applications earlier Wednesday.

While the bids were warmly received by most allies, Turkey, which like all NATO members has the right to veto a nation's candidacy, has raised objections, and ambassadors meeting in Brussels failed to reach consensus on starting formal membership negotiations.

Historically non-aligned, Sweden and Finland have made a 180-degree turn since Russia's invasion of Ukraine, an event that drastically swayed opinion among a general public that had formerly been reluctant to join the alliance.