Finland has decided to seek NATO membership in the next few days, President Sauli Niinisto told Saturday his Russian counterpart Vladimir Putin, who replied that Helsinki's move to ditch its long-established military neutrality would be a mistake.

Niinisto’s office said in a statement that the Finnish head of state told Putin in a phone conversation how thoroughly Finland’s security environment had changed after Moscow’s Feb. 24 invasion of Ukraine, and pointed to Russia’s demands regarding Finland refraining from seeking membership in NATO, the 30-member Western military alliance.

"The discussion (with Putin) was straightforward and unambiguous and was held without exaggeration. Avoiding tensions was considered important," said Niinisto, Finland’s president since 2012 and one of the few Western leaders who has held a regular dialogue with Putin over the past 10 years.

Niinisto pointed out that had already told Putin at their first meeting in 2012 that "each independent nation would maximize its own security."

"That is still the case. By joining NATO, Finland will strengthen its own security and assume its responsibilities. It is not something away from anybody," Niinisto said.

He stressed that Finland, despite its likely future membership in NATO, wants to continue to deal with Russia bilaterally in "practical issues generated by the border neighborhood" and hopes to engage with Moscow "in a professional manner."

The phone call was conducted on Finland's initiative, Niinisto's office said.

The Kremlin later said: "Vladimir Putin stressed that abandoning the traditional policy of military neutrality would be a mistake since there are no threats to Finland's security. Such a change in the country's foreign policy may have a negative impact on Russian-Finnish relations."

Moscow described the call as a "frank exchange of views," normally a diplomatic euphemism for a difficult conversation.

Finland shares a 1,340-kilometer (830-mile) border with Russia, the longest by any European Union member.

Niinisto and Finnish Prime Minister Sanna Marin on Thursday jointly endorsed Finland’s NATO bid and recommended that the country "must apply for NATO membership without delay" to guarantee the nation’s security amid Russia's military maneuvers in Ukraine and Europe's changing geopolitical and security landscape.

A formal announcement from Niinisto and Marin that Finland intends to apply for NATO membership is expected on Sunday, a day after the likely endorsement by Marin’s governing Social Democratic party.

Neighboring Sweden is likely to decide on its NATO stance on Sunday in a meeting of the governing Social Democratic Party led by Prime Minister Magdalena Andersson.

U.S. President Joe Biden held a joint call Friday with both Niinisto and Andersson where, according to a White House statement, he "underscored his support for NATO’s Open Door policy and for the right of Finland and Sweden to decide their own future, foreign policy and security arrangements."

The U.S. is also working with Turkey on the NATO membership of the two nations, the White House said, after President Recep Tayyip Erdoğan voiced Ankara's objection over Helsinki and Stockholm's welcoming stance toward the PKK and other terrorist groups.