Russia has appeared to threaten nuclear deployment if NATO bases appear in Finland or Sweden.
Finland will apply for membership in the NATO military alliance, the country's president Sauli Niinisto confirmed on Sunday.
It is a historic policy shift largely prompted by Russia's invasion of Ukraine.
According to the BBC, Russian state TV said on Finland and Sweden wanting to join Nato: "Their official reason is fear. But they’ll have more fear in Nato.
"When Nato bases appear in Sweden & Finland, Russia will have no choice but to neutralise the imbalance & new threat by deploying tactical nuclear weapons."
Moscow, which shares a 1,300km border with Finland, has said it would be a mistake for Helsinki to join the 30-strong transatlantic alliance and that it would harm bilateral ties.
Vladimir 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 on Sunday about his call.
Sweden is also expected to follow suit as public support for membership has grown amid security concerns.
Sunday's announcement comes after Niinisto and Finland's prime minister, Sanna Marin, said on Thursday they both favoured membership in NATO (the North Atlantic Treaty Organisation), 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 Russian President Vladimir Putin on Saturday to tell him of Finland's plans to join the alliance.
Putin said he thought the move would be a mistake, but did not repeat earlier threats that any such move would trigger countermeasures from Moscow, the Finnish leader said in an interview with CNN on Sunday.
"Altogether, the discussion was very, would I say, calm and cool," Niinisto said. "The surprise was that he took it so calmly."
However, he added: "You have to keep in mind that what he said doesn't mean that you shouldn't be all the time quite, well, aware and follow up what really is happening. But so far, it seems that there's no immediate problems coming."
The Finnish president expressed readiness to hold talks with his Turkish counterpart Tayyip Erdogan after Ankara raised objections to the Nordic countries joining NATO.
As a NATO member, Turkey could veto their applications. Niinisto said he was "a bit confused" about what he said was a shift in Turkey's stance. "What we need now is a very clear answer, I am prepared to have a new discussion with President Erdogan about the problems he has raised."
He told CNN he believed there will be a lot of discussion on the matter. "I'm not that worried about that," Niinisto said.
