Finland formally joined the NATO military alliance on Tuesday in a historic policy shift brought on by Russia's invasion of Ukraine, drawing a threat from Moscow of "countermeasures."
Finland's accession roughly doubles the length of the border that NATO shares with Russia and bolsters its eastern flank as the war in Ukraine grinds on with no resolution in sight.
Finnish Foreign Minister Pekka Haavisto completed the accession process by handing over an official document to US Secretary of State Antony Blinken at NATO headquarters in Brussels.
NATO Secretary-General Jens Stoltenberg, welcoming Finland to its ranks, noted that Russian President Vladimir Putin had cited opposing NATO expansion as one justification for his invasion.
"He is getting exactly the opposite... Finland today, and soon also Sweden will become a full-fledged member of the alliance," Stoltenberg said in Brussels.
The Kremlin said Russia would be forced to take "counter-measures" to Finland's accession. Defense Minister Sergei Shoigu said the move raised the prospect of the conflict in Ukraine escalating further.
Russia said on Monday it would strengthen its military capacity in its western and northwestern regions in response to Finland joining NATO.
The Ukrainian government also hailed Finland's move. President Volodymyr Zelensky's chief of staff Andriy Yermak wrote on Telegram: "FI made the right choice. NATO is also a key goal for Ukraine."
The event marks the end of an era of military non-alignment for Finland that began after the country repelled an invasion attempt by the Soviet Union during World War Two and opted to try to maintain friendly relations with neighboring Russia.
But the invasion of Ukraine in February 2022 prompted Finns to seek security under NATO's collective defense pact, which states that an attack on one member is an attack on all.
Moscow, which has long criticized the move, reacted crossly.
Kremlin spokesman Dmitry Peskov said the NATO expansion was an "encroachment on our security and on Russia's national interests." Moscow would watch closely for any NATO military deployments in Finland, he said.
"I'm tempted to say this is maybe the one thing we can thank Mr. Putin for. Because he once again here precipitated something he claims to want to prevent."
Joe Biden
Blinken said: "I'm tempted to say this is maybe the one thing we can thank Mr. Putin for. Because he once again here precipitated something he claims to want to prevent."
Sweden's quest to join NATO continues
Sweden and Finland applied together last year to join NATO, but the Swedish application has been held up by NATO members Turkey and Hungary.
Swedish Foreign Minister Tobias Billstroem told reporters it was Stockholm's ambition to become a member at the NATO summit in Vilnius in July.
"This is a question of utmost importance for Sweden... There is no reason for neither the Turkish parliament or the Hungarian parliament to make any further delays," he said.
Turkey says Stockholm harbors members of what Ankara considers terrorist groups - an accusation Sweden denies - and has demanded their extradition as a step toward ratifying Swedish membership.
Hungary cites grievances over criticism of Prime Minister Viktor Orban's democratic record. NATO diplomats say they expect Budapest to approve Sweden's bid if it sees Turkey moving to do so.
Finland will work "relentlessly" to secure Sweden's membership of NATO, Finnish President Sauli Niinisto said on Tuesday, shortly after his own country formally became the 31st country to join the Atlantic alliance.
"Finland's membership is not complete without Swedish membership. The work for Sweden's early membership continues relentlessly," Niinisto said in a statement.
Finland and Sweden applied together to join NATO following Russia's invasion of Ukraine in February 2022. Of NATO's existing members, Hungary and Turkey have still to ratify Sweden's membership application.
Ending military non-alignment
The event marks the end of an era of military non-alignment for Finland that began after the country repelled an invasion attempt by the Soviet Union during World War Two and opted to try to maintain friendly relations with neighbouring Russia.
But the invasion of Ukraine in February 2022 prompted Finns to seek security under NATO's collective defence pact, which states that an attack on one member is an attack on all.
Moscow, which has long criticised the move, reacted crossly.
Kremlin spokesman Dmitry Peskov said the NATO expansion was an "encroachment on our security and on Russia's national interests". Moscow would watch closely for any NATO military deployments in Finland, he said.
Since the end of the Cold War three decades ago, Moscow has watched successive waves of NATO enlargement to the formerly communist east of Europe with consternation, and the issue was a bone of contention even before the invasion of Ukraine.
NATO has repeatedly stressed that it is solely a defensive alliance and does not threaten Russia.
Blinken said: "I'm tempted to say this is maybe the one thing we can thank Mr Putin for. Because he once again here precipitated something he claims to want to prevent."
Finland and its Nordic neighbour Sweden applied together last year to join NATO, but the Swedish application has been held up by NATO members Turkey and Hungary.
Swedish Foreign Minister Tobias Billstroem told reporters it was Stockholm's ambition to become a member at the NATO summit in Vilnius in July.
"This is a question of utmost importance for Sweden...There is no reason for neither the Turkish parliament or the Hungarian parliament to make any further further delays," he said.
Turkey says Stockholm harbours members of what Ankara considers terrorist groups - an accusation Sweden denies - and has demanded their extradition as a step toward ratifying Swedish membership.