Finland will apply to join NATO despite Russian president Vladimir Putin 's grave warning that it would be a mistake.
President Sauli Niinisto confirmed his country would submit an application for the military alliance in a historic policy shift prompted by Russia's invasion of Ukraine.
Moscow, which shares a 1,300 km (800 mile) border with Finland, has said it would be a mistake for Helsinki to join the transatlantic alliance and that it would harm bilateral ties.
Sweden is also expected to follow suit as public support for membership has grown due to security concerns.
Sunday's announcement comes after Niinisto and Prime Minister Sanna Marin said on Thursday they both favoured NATO (North Atlantic Treaty Organisation) membership, giving a green light for the country to apply.
"Today, we, the president and the government's foreign policy committee, have together decided that Finland...will apply for NATO membership," Niinisto told reporters in the presidential palace in Helsinki.
Niinisto called Putin on Saturday to tell him of Finland's plans to join the alliance.
Putin said such a move would hurt Russian-Finnish relations.
"I, or Finland, are not known to sneak around and quietly disappear behind a corner. It is better to say it straight what already has been said, also to the concerned party and that is what I wanted to do," he said about his call on Sunday.
It comes after Russia confirmed it will take precautionary measures if NATO deploys nuclear forces closer to its borders, according to the country's deputy foreign minister.
Alexander Grushko added that Moscow has no hostile intentions towards Finland and Sweden.
But he said he doesn't see "real" reasons for the two countries to join the alliance.
"It will be necessary to respond...by taking adequate precautionary measures that would ensure the viability of deterrence," Interfax agency quoted Grushko as saying.
Kremlin forces invaded Ukraine on February 24.
Putin has demanded the former-Soviet allies never be allowed to become a member of the alliance.
The southeastern region of Donbas has become the main theatre of war over the past month.
Ukraine's counteroffensive there is underway near the Russian-held town of Izium, but its military has reported that Moscow forces are advancing elsewhere.
Having resisted fiercely since Russia launched its invasion 11 weeks ago, Ukraine's military has notched a string of successes, first forcing Russia's commanders to abandon an advance on the capital Kyiv, and then making rapid gains in the northeast in recent week to drive the enemy away from the second biggest city of Kharkiv.
Since mid-April, Russian forces have focussed much of their firepower on the east for what has become known as the "Battle of the Donbas".
British military intelligence delivered a damning assessment on Sunday of Russia's campaign in the region.
It reckoned that Russia had lost about a third of the ground combat force deployed in February, and its offensive in the Donbas had fallen "significantly behind schedule" and was unlikely to make rapid advances during the coming 30 days.
Keeping up pressure on Izium and Russian supply lines will make it harder for Moscow to encircle battle-hardened Ukrainian troops on the eastern front in the Donbas.
