BRUSSELS -- The blue-and-white Finnish flag rises outside NATO headquarters this afternoon, making Finland a member and doubling Russia's border with the world's biggest security alliance.
The move is a strategic and political blow to President Vladimir Putin, who has long complained about NATO's expansion toward Russia and partly used that as a justification for his country's war with Ukraine.
"What we see is that President Putin went to war against Ukraine with a declared aim to get less NATO," NATO Secretary-General Jens Stoltenberg said. "He's getting the exact opposite."
Like all NATO members, Finland will benefit from the collective security guarantee that an attack on one is considered an attack on all.
NATO has said that it has no immediate intention to step up its presence in Finland. Some members have deployed troops there for war games over the last year.
Russia immediately warned that it would bolster forces near Finland if NATO sends any additional troops or equipment to what will be its 31st member country
Finland has substantial, well-trained armed forces with elite troops capable of operating in the sub-zero temperatures of the high north. The Nordic country also has a large reserve army and is investing heavily in new equipment, including dozens of U.S.-made F-35 fighter jets.
The ceremony to raise the Finnish flag between the French and the Estonian flags is scheduled for 9:30 a.m. EST will complete the fastest accession process in the organization's recent history.
Alarmed by Russia's invasion of Ukraine last year, Finland applied to join NATO in May 2022. Neighboring Sweden also applied, but its accession process will take longer.
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 will be a good day for Finland's security, for Nordic security, and for NATO as a whole," Stoltenberg told reporters on Monday on the eve of a meeting of alliance's foreign ministers in Brussels.
Russia's Deputy Foreign Minister Alexander Grushko warned that Moscow would bolster its own forces "in case of deployment of forces of other NATO members on the territory of Finland."
"We will strengthen our military potential in the west and in the northwest," Grushko said, according to the state RIA Novosti news agency, although Russia is already having trouble marshaling forces against far-smaller Ukraine.
Finland shares a 832-mile border with Russia and unlike most members of the alliance, Finland did not cut defense spending and investment after the Cold War.
"They have trained and built a large army over many years and maintain that high level of readiness. Finland is also a country with extremely high level of resilience, of preparedness throughout the whole society," Stoltenberg said.
The country also helps to complete NATO's geographical puzzle by filling in a major gap in the strategically important Baltic Sea region in Europe's north.
Last week, Stoltenberg said, Turkey, the last country to have ratified Finland's membership, will hand the official document enshrining its approval to U.S. Secretary of State Antony Blinken.
NATO's top civilian official said he will then invite Finland to hand over its own signed documents, to complete the procedure.
Finnish President Sauli Niinisto and Defense Minister Antti Kaikkonen will attend the flag-raising ceremony along with Foreign Minister Pekka Haavisto.
"It is a historic moment for us. For Finland, the most important objective at the meeting will be to emphasize NATO's support to Ukraine as Russia continues its illegal aggression," Haavisto said in a statement. "We seek to promote stability and security throughout the Euro-Atlantic region."
Information for this article was contributed by Jari Tanner of The Associated Press.
NATO Secretary General Jens Stoltenberg speaks during a media conference, ahead of a meeting of NATO foreign ministers, at NATO headquarters in Brussels, Monday, April 3, 2023. (AP Photo/Geert Vanden Wijngaert)