Finland must apply to join the NATO military alliance "without delay", Finnish President Sauli Niinisto and Prime Minister Sanna Marin said on Thursday, a major policy shift triggered by Russia's invasion of Ukraine.
Finland, which shares a 1,300 km (810 mile) border and a difficult past with Russia, has gradually stepped up its cooperation with the North Atlantic Treaty Organization as a partner since Russia annexed Crimea in 2014.
But until Russia's invasion of Ukraine, the Nordic country had refrained from joining in order to maintain friendly relations with its eastern neighbour.
"Finland must apply for NATO membership without delay," Niinisto and Marin said in a joint statement.
"We hope that the national steps still needed to make this decision will be taken rapidly within the next few days."
NATO allies expect Finland and Sweden to apply to join the alliance in the coming days and will grant membership quickly, five diplomats and officials told Reuters ahead of the Finnish announcement.
Baltic countries, which were once ruled from Moscow and are now members of NATO, welcomed Finland's announcement.
"Finland decided to join the Alliance. NATO is about to get stronger. Baltics about to get safer," Lithuanian Foreign Minister Gabrielius Landsbergis said.
The view among Finns on NATO has changed rapidly since Russia initiated what it calls a "special operation" in Ukraine.
Finnish public support for joining NATO has risen to record numbers over recent months, with the latest poll by public broadcaster YLE showing 76% of Finns in favour and only 12% against, while support for membership used to linger at only around 25% for years prior to the war in Ukraine.
While military non-alignment has long satisfied many Finns as a way of staying out of conflicts, Russia's invasion of sovereign Ukraine has led an increasing number of Finns to view friendly relations with Russia as an empty phrase.
Ukraine's fate has been particularly disturbing for Finland to watch as it fought two wars with Russia between 1939 and 1944, repelling an attempted invasion but losing around 10% of its territory in the subsequent peace agreement.
Finland's rapid shift towards NATO is likely to pull along neighbouring Sweden.
Sweden's ruling Social Democrats are expected to decide on Sunday whether to overturn decades of opposition to NATO membership, a move that would almost certainly lead to Sweden also asking to join the 30-nation alliance.
Russia has repeatedly warned both countries against joining the alliance. As recently as March 12 its foreign ministry said "there will be serious military and political consequences" if they do.
The speed of the Finnish decision to apply has come as a surprise to many, with most political discussions taking place behind the scenes out of fear over Russia's reaction.
In March, Finland's government initiated a security policy review and delivered a report for parliament to discuss in April, while also holding discussions with all parliamentary groups to secure backing for the decision to join the treaty.
In parallel with the domestic process, Finland's president and prime minister have toured NATO countries to win their support for Finland's membership.
NATO Secretary-General Jens Stoltenberg has previously said it would be possible to allow Finland and Sweden to join "quite quickly".
