Less than three months after Russia's February 24 invasion of Ukraine, the move is a stunning reversal of Finland's policy on military non-alignment dating back more than 75 years.

Sweden, which has been militarily non-aligned for more than two centuries, is also seen following suit, with a similar announcement expected on Monday.

"Today, the President of the Republic and the Government's Foreign Policy Committee have jointly agreed that Finland will apply for NATO membership, after consulting parliament. This is a historic day. A new era is opening", Finnish President Sauli Niinisto told reporters on Sunday.

Despite last-minute objections voiced by Turkey, NATO members are on "good track" in their discussions on welcoming Sweden and Finland into the Western military alliance, Croatia's foreign minister, Gordan Grlic Radman, said as he arrived for talks with NATO counterparts in Berlin.

Finland's parliament will convene to debate the membership proposal on Monday.

"We hope the parliament will confirm the decision to apply for NATO membership during the coming days. It will be based on a strong mandate", Prime Minister Sanna Marin said.

An overwhelming majority of Finnish MPs back the decision, after Marin's Social Democratic Party on Saturday said it was in favour of membership.

"Hopefully we can send our applications next week together with Sweden," Marin said on Saturday.

The two Nordic countries broke their strict neutralities after the end of the Cold War by joining the EU and becoming partners to NATO in the 1990s, solidifying their affiliation with the West.

But the concept of full NATO membership was a non-starter in the countries until the war in Ukraine saw public and political support for joining the military alliance soar.

Finland, which shares a 1,300-kilometre (800-mile) border with Russia, has been leading the charge, while Sweden appears anxious at being the only non-NATO country around the Baltic Sea.

Many Swedish politicians have even said their support is conditional on Finland joining.

On Saturday, the Finnish head of state phoned his Russian counterpart President Vladimir Putin to inform him of his country's desire to join NATO, in a conversation described as "direct and straightforward".

"Avoiding tensions was considered important," Niinisto was quoted as saying in a statement by his office.

But Putin responded by warning that joining NATO "would be a mistake since there is no threat to Finland's security", according to a Kremlin statement.

On Sunday, Niinisto said that while Finland expects Russia to respond to its decision, "little by little, I'm beginning to think that we're not going to face actual military operations."

"After the phone call with Putin, I think so even more."

- No other choice -

According to recent polls, the number of Finns who want to join the alliance has risen to over three-quarters, almost triple the level seen before the war in Ukraine.

In Sweden, support has also risen dramatically, to around 50 percent -- with about 20 percent against.

The senior leadership of Sweden's Social Democrats, led by Prime Minister Magdalena Andersson, is due to meet on Sunday afternoon to decide whether the party should abandon its historic stance against joining, last reaffirmed at the party's annual congress in November.

A green light from the ruling Social Democrats would secure a firm majority in Sweden's parliament in favour of joining.

While the party's leading politicians have seemed ready to reverse the decision, critical voices within have denounced the change in policy as rushed.

But analysts say it is unlikely that the party will oppose the move.

"There will perhaps not be the same sense of urgency," as in Finland, defence researcher Robert Dalsjo, an analyst at the Swedish Defence Research Institute (FOI), told AFP.

"But the leaders in Sweden have realised that they really don't have another choice, once Finland has," he added.

NATO membership needs to be approved and ratified by all 30 members of the alliance.

While Finland and Sweden claim to have had favourable signals from Ankara, Turkish President Recep Tayyip Erdogan has expressed his opposition.

Turkey's objections, directed in particular at Stockholm, focus on what it considers to be the countries' leniency towards the Kurdistan Workers' Party (PKK), which is on the EU's list of terrorist organisations.

However, Turkish Foreign Minister Mevlut Cavusoglu said he was ready to discuss the matter with both countries, as well as with other NATO nations.

Finnish Foreign Minister Pekka Haavisto said he was "confident" of reaching an agreement with Turkey.