Finland is set to officially become a member of NATO later on Tuesday and take its place among the ranks of the world’s biggest security alliance.

Neighboring Russia has already warned that it will bolster its defences near their joint border if NATO deploys any additional troops or equipment to what will be its 31st member country.

Finland’s blue and white flag is scheduled to be raised among those of its partners outside NATO’s Brussels headquarters. Finland’s president, and foreign and defense ministers will take part.

The ceremony falls on NATO’s very own birthday, the 74th anniversary of the signing of its founding Washington Treaty on April 4, 1949. It also coincides with a meeting of the alliance’s foreign ministers.

Turkey became the last NATO member country to ratify Finland’s membership protocol on Thursday. It will hand over the document officially enshrining that decision to US Secretary of State Antony Blinken before the ceremony.

Finland will then give Blinken its own final texts, officialising its membership.

Alarmed by Russia’s invasion of Ukraine last year, Finland applied to join NATO in May 2022, setting aside years of military nonalignment to seek protection under the organization’s security umbrella. Neighbouring Sweden also applied, but its accession process may take a few months longer.

Finland shares a 1,340-kilometer (832-mile) border with Russia, so its entry will more than double the size of NATO’s border with Russia.

The move is a strategic and political blow to Russian President Vladimir Putin, who has long complained about NATO’s expansion toward Russia.

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