Russia-Ukraine war: Vladimir Putin warns Finland it would be 'a mistake' to join Nato

Vladimir Putin spoke to Finnish President Sauli Niinisto about Helsinki's plans to join Nato. Photo / AP

Vladimir Putin warned Finland it was making a "mistake" joining Nato, saying relations would be "negatively affected" if Helsinki ended decades of military neutrality.

The Russian president made the thinly-veiled threat after Sauli Niinisto, the president of Finland, spoke to him by phone to confirm that Helsinki would apply to join the alliance in the next few days.

Putin has previously demanded that Finland and Sweden never join Nato, and invaded Ukraine in order to stop it from doing the same despite the low likelihood of it being granted membership.

Earlier this week, Russia's foreign ministry said it would be forced to take "retaliatory steps" including military action if Finland and Sweden went ahead with their Nato applications.

On Saturday, Alexander Grushko, the deputy foreign minister, said Moscow would respond and take "adequate precautionary measures" if Nato deployed nuclear forces and infrastructure closer to Russia's border.

What exactly it would do is not clear, but some repercussions are already emerging.

A Russian energy supplier shut off electricity supplies to Finland, and there are concerns that gas supplies could also be affected in the future. Russia provides about 10 per cent of Finland's electricity.

Members of a pro-Kremlin patriotic youth club wear World War II-era Soviet military uniforms with the letter Z attached, which has become a symbol of the Russian military in the Ukraine conflict. Photo / AP

One Russian lawmaker went as far as threatening Finland with nuclear attack if it joined Nato and warned that Moscow's "absolutely legitimate goal" would be "to question the very existence of this state".

"They are going to become a target for the Russian military, this is for sure," said Alexei Zhuravlyov, a pro-Kremlin politician.

He threatened to use Russia's new Sarmat hypersonic nuclear missile against Britain and northern Europe in a warning shot across Finland's bows.

"If Finland decides to join this bloc, our goal, an absolutely legitimate one, will be to question the very existence of this state," he told the Ura.ru website.

Putin was less bombastic in his call with Mr Niinisto on Saturday, which was initiated by Finland. However, he warned Helsinki that the abandonment of "its 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 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," a Kremlin statement quoted him as saying.

But Niinisto said Russian threats over joining Nato and Putin's "massive invasion" of Ukraine had fundamentally altered Finland's "security environment".

"The discussion was straightforward and unambiguous and was held without exaggeration. Avoiding tensions was considered important," said Finland's president since 2012 and one of a handful of Western leaders who has been in regular dialogue with Putin over the past decade.

Members of a pro-Kremlin patriotic youth club march with a mourning flower garland during a youth honour guards competition. Photo / AP

Finland shares a 1336km border with Russia and, like Ukraine, is not a Nato member and does not benefit from its protections.

"By joining Nato, Finland will strengthen its own security and assume its responsibilities. It is not something away from anybody," Niinisto said. He added that he hoped to engage with Moscow "in a professional manner" in the future.

Putin precipitated a seismic shift in attitudes towards Nato membership in historically non-aligned Finland and Sweden when he ordered the invasion of Ukraine.

Finland has been neutral since its invasion by the Soviet Union in World War II. Sweden has been non-aligned for more than 200 years. Both countries stayed out of Nato, which was founded in 1949 to counter the Soviet Union, during the cold war.

With public support for joining Nato never higher, both are expected to apply to join the military alliance soon and bolster its defence with their well-equipped modern forces.

Both countries signed mutual defence pacts with the UK this week, which could mean British troops being sent to defend them if Russia was to attack the Nordic nations.

Niinisto and Finnish Prime Minister Sanna Marin have called for Finland to apply to Nato, which guarantees an attack on one member is one on all 30 members, "without delay". A formal announcement is expected early next week.

Vladimir Putin spoke to Finnish President Sauli Niinisto about Helsinki's plans to join Nato. Photo / AP

Both Finland and Sweden, which are attending a meeting of Nato foreign ministers in Berlin on Sunday, are expected to apply and join at the same time.

Nato has said it will make the process as quick and smooth as possible. However, Turkey said it was not yet sure if it would back Finland and Sweden's bids. Any country joining must have the unanimous support of all existing members.

On Saturday, Ankara said it had not shut the door the idea. President Tayyip Erdogan's spokesman said Ankara wanted negotiations with the Nordic countries and a clampdown on what it sees as pro-Kurdish terrorist activities.