Russian President Vladimir Putin told his Finnish counterpart Sauli Niinisto on Saturday that ditching neutrality and joining NATO would be a mistake that could damage relations between their two countries, the Kremlin said.
The two countries said their presidents spoke by phone two days after Finland declared its intention to join the Western alliance. Moscow has described that as a security threat that will require it to respond, but has not specified how.
Niinisto's office said he told 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".
He said Finland wanted to handle relations with its Russian neighbour in a "correct and professional manner".
The Kremlin 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.
Niinisto said: "The conversation was direct and straightforward and it was conducted without aggravations. Avoiding tensions was considered important."
Finland's membership bid is expected to be followed by a similar move from Sweden, confronting Putin with exactly what he said he wanted to avoid when he launched his invasion of Ukraine on Feb 24: a further expansion of NATO to Russia's borders.