HELSINKI, Finland and Sweden will submit their bids to join NATO together Wednesday, the two Nordic countries announced on Tuesday.

"I'm happy we have taken the same path and we can do it together," Swedish Prime Minister Magdalena Andersson said Tuesday during a joint press conference with Finnish President Sauli Niinisto.

Their applications will culminate decades of military non-alignment to join the alliance as a defense mechanism.

Russian President Vladimir Putin warned Monday NATO's expansion may trigger a response from Moscow.

But the main obstacle to their membership comes from within the alliance despite NATO Secretary General Jens Stoltenberg repeatedly insisting the two countries would be welcomed "with open arms".

Turkey has insisted that Ankara will not approve expansion. Any membership bid must be unanimously approved by NATO's 30 members.

Niinisto said Tuesday he was "optimistic" Finland and Sweden would be able to secure Turkey's support.

Andersson and Niinisto are to meet U.S. President Joe Biden in Washington Thursday to discuss their historic bids.

After a marathon debate lasting a day-and-a-half, 188 out of 200 Finnish lawmakers voted in favour of NATO membership, a dramatic reversal of Finland's military non-alignment policy dating back more than 75 years.

"Our security environment has fundamentally changed," Finnish Prime Minister Sanna Marin told parliament Monday at the start of the debate.