The phone call, which was "initiated by Finland... was direct and straight-forward and it was conducted without aggravations. Avoiding tensions was considered important," Niinisto was quoted as saying in a statement by his office.

But the Kremlin responded by saying that Putin viewed any end to Finland's military neutrality as a "mistake."

"Putin stressed that the end of the traditional policy of military neutrality would be a mistake since there is no threat to Finland's security," it said in a statement.

"Such a change in the country's political orientation can have a negative impact on Russian-Finnish relations developed over years in a spirit of good neighbourliness and cooperation between partners," the Kremlin added.

Finland is expected to officially announce its NATO membership bid on Sunday.

The Nordic country and eurozone member "wants to take care of the practical questions arising from being a neighbour of Russia in a correct and professional manner," said Niinisto, who has communicated regularly with Putin in recent years.

Moscow's February 24 invasion of Ukraine has swung political and public opinion in Finland and neighbouring Sweden in favour of NATO membership as a deterrent against Russian aggression.

Both countries have long cooperated with the Western military alliance and are expected to be able to join it quickly.

Sweden, like Finland traditionally neutral, is also expected to announce its own NATO membership bid in the coming days.

NATO chief Jens Stoltenberg has repeatedly said they would be welcomed "with open arms".

- Electricity supply suspended -

The Finnish president and Prime Minister Sanna Marin had said on Thursday that they wanted the country to join NATO "without delay" and that a membership bid was expected to be announced on Sunday.

Moscow responded by saying it would "definitely" see Finnish membership as a threat and that Moscow would be "forced to take reciprocal steps, military-technical and other, to address the resulting threats".

On Saturday, the Finnish grid operator said that Russia suspended electricity supplies to Finland overnight after its energy firm RAO Nordic threatened to cut off supplies over payment arrears.

"It is at zero at the moment, and that started from midnight as planned," Timo Kaukonen, manager for operational planning at Fingrid, said.

Nevertheless, Finland -- which only imports about 10 percent of its power from Russia -- said the shortfall was being made up by imports from Sweden.

RAO Nordic says it has not been paid for electricity since May 6 but has not spelt out if this was linked to European sanctions against Russia.

According to Helsinki, Niinisto 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".

Already on Thursday, Niniisto had told Russia: "You caused this. Look in the mirror."

After Finland's NATO membership bid is officially announced on Sunday, it will be discussed by parliament on Monday.