Finland's President Sauli Niinistö has formally notified Vladimir Putin of the country's application to join NATO, in a phone call on Saturday.
The militarily non-aligned Nordic country that shares a long border and history with Russia “will decide to apply for NATO membership in the coming days”, said a statement from the president's office.
"President Niinistö told President Putin how fundamentally the Russian demands in late 2021 aiming at preventing countries from joining NATO and Russia’s massive invasion of Ukraine in February 2022 have altered the security environment of Finland," the statement explained.
“The conversation was direct and straight-forward and it was conducted without aggravations. Avoiding tensions was considered important”, President Niinistö said.
The Kremlin responded by saying that relations between the two neighbours could be “negatively affected" if Finland follows through with plans to apply for NATO membership.
Niinistö has been Finland’s president since 2012 and is one of few Western leaders who has held regular dialogue with Putin over the past ten years.
He said he had told the Russian leader that Finland was seeking to strengthen its security by joining NATO, and still wanted to engage with Moscow practically and professionally.
The phone call was conducted on Finland's initiative, Niinistö's office said.
The Kremlin's press service said in a statement that Putin told Sauli Niinistö that Finland's abandonment “of its traditional policy of military neutrality would be an error since there are no threats to Finland’s security”.
“Such a change in the country’s foreign policy could negatively affect Russian-Finnish relations, which had been built in the spirit of good neighbourliness and partnership for many years, and were mutually beneficial,” the statement added.
Finland shares a 1,340-kilometre border with Russia, the longest by any European Union member. Applying to join NATO is a historic development: Finland adopted neutrality after being defeated by the Soviet Union in World War II.
Russia's electricity exports to Finland stopped overnight on Friday after a Russian supplier announced the move earlier, an official at Finland's power grid operator said.
The company responsible for Russian electricity sales to Finland, RAO Nordic, cited unpaid bills as the reason for the decision, though it is being linked to the move to join NATO.
Niinistö and Finnish Prime Minister Sanna Marin jointly endorsed Finland’s NATO bid on Thursday and recommended that the country “must apply for NATO membership without delay”.
"NATO membership would strengthen Finland's security. As a member of NATO, Finland would strengthen the entire defence alliance," they said.
Meanwhile neighbour Sweden is also expected to decide on Sunday whether it will ask to join NATO, at a meeting of the governing Social Democratic Party led by Prime Minister Magdalena Andersson.
US President Joe Biden held a joint call Friday with both Niinistö and Andersson. 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”.