Rattled by Russia’s invasion of Ukraine, Finland’s prime minister said Wednesday the Nordic nation would decide whether to apply for NATO membership “within weeks”, despite the risk of infuriating Moscow.

Helsinki’s parliament will next week open a debate about joining the Western alliance after the Ukraine war sparked a dramatic U-turn in public and political opinion in Finland and neighbouring Sweden over long-held policies of military non-alignment.

Attempting to join NATO would almost certainly be seen as a provocation by Moscow, for whom NATO’s expansion on its borders has been a prime security grievance.

But Prime Minister Sanna Marin said Finland would now decide quickly on whether to apply for membership of the North Atlantic Treaty Organization.

“I think it will happen quite fast. Within weeks, not within months,” Marin told a Stockholm press conference with Swedish Prime Minister Magdalena Andersson.

Sweden is also discussing NATO membership following Russia’s February 24 invasion.

– Guarantees –

A Finnish government-commissioned report released Wednesday examined the “fundamentally changed” security environment, according to the foreign ministry, and will make its way through parliament.

The report did not make recommendations but stressed, as did Marin in her speech, that without NATO membership Finland enjoys no security guarantees, despite being a partner to the alliance.

“There is no other way to have security guarantees than under NATO’s deterrence and common defence as guaranteed by NATO’s Article 5,” Marin said, referring to an attack on one member being considered an attack on all.

The “deterrent effect” on Finland’s defence would also be “considerably greater” inside the alliance, the report noted while adding it also carried obligations for Finland to assist other members.

An opening parliamentary debate on membership is set for next Wednesday.

Former prime minister and long-time NATO advocate Alexander Stubb said he believes a membership application is “a foregone conclusion”.

Finland has a long history with Russia. In 1917 it declared independence after 150 years of Russian rule.

During World War II, its vastly outnumbered army fought off a Soviet invasion, before a peace deal saw it cede several border areas to Moscow.

During the Cold War, Finland remained neutral in exchange for guarantees from Moscow that it would not invade.

– Change of heart –

The turnaround in sentiment on NATO would have been unthinkable just a few months ago.

As recently as January, Prime Minister Marin had said membership was “very unlikely” during her term.

But after two decades of public support for membership remaining steady at 20-30 percent, the war caused a surge in those in favour to over 60 percent.

Public statements gathered by newspaper Helsingin Sanomat suggest half of Finland’s 200 MPs now support membership while only 12 oppose.

Others say they will announce a position after detailed discussions.

The government said it hopes to build a parliamentary consensus over the coming weeks, with MPs due to hear from a number of security experts.

Many analysts predict Finland could submit a bid in time for a NATO summit in June.

Any membership bid must be accepted by all 30 NATO states, a process that could take four months to a year.

Finland has so far received public assurances from secretary general Jens Stoltenberg that NATO’s door remains open, and support from several members.

– ‘Like changing religion’ –

Unlike Finland, Sweden shares no land border with Russia and the two countries have not been at war for two centuries.

Nonetheless, pro-NATO sentiment is also rising among Swedes who “are realising that they might find themselves in the same position as Ukraine, a lot of sympathy but no military help”, said Robert Dalsjo, research director at the Swedish Defence Research Agency.

Many commentators expect Sweden and Finland will act in tandem on whether to join, but their leaders have stressed they may reach differing decisions.

Sweden’s ruling party this week announced a review of its long-held opposition to joining NATO.

“For the Social Democrats in Sweden to change opinion (on NATO) is like changing religion,” ex-PM  Stubb told AFP.

“And I’m not talking Protestant to Catholic, I’m talking Christian to Muslim.”

Kremlin spokesman Dmitry Peskov warned Russia would take measures to “rebalance the situation” if  Finland joined.

President Sauli Niinisto said Russia’s response could include airspace, territorial violations and hybrid attacks, which Finnish NATO proponents believe the country is well prepared to withstand.

Wednesday’s report  stated that even as a member, “Finland’s goal would be to maintain functioning relations with Russia.”

“Russia will most certainly huff and puff,” Dalsjo said, but added: “I don’t think they will do anything violent.

“However, in the mood that (Russian President Vladimir) Putin is right now, I wouldn’t rule it out entirely.”