Politicians in Finland are due to start debating whether the country should seek membership in the NATO military alliance after Russia’s invasion of Ukraine prompted a spike in political and public support for joining the transatlantic bloc.

The parliament session on Wednesday comes despite warnings by Russia of a nuclear buildup in the Baltic should Finland and neighbouring Sweden join NATO.

"I think it will happen quite fast. Within weeks, not within months,” Finland’s Prime Minister Sanna Marin said last week, referring to her country deciding on whether to apply for membership.

Finland’s 200 members of parliament have received a government-commissioned "white paper” that assessed the implications of NATO membership alongside other security options, such as increased bilateral defence agreements.

The report does not make recommendations but stresses that without NATO membership Finland – a European Union member state that shares a 1,300km (810-mile) border with Russia – enjoys no security guarantees, despite currently being a partner of the alliance. It also says the "deterrent effect” on Finland’s defence would be "considerably greater” inside the bloc, while noting that membership also carried obligations for Finland to assist other NATO states.

Sweden is also discussing whether to submit a membership bid following Russia’s February 24 invasion. A poll on Wednesday showed that 57 percent of Swedes now favoured NATO membership, up from 51 percent in March. Those opposed to joining fell to 21 percent from 24 percent, while those who were undecided dipped to 22 percent from 25 percent.

‘Highly likely’

In Finland, after two decades of public support for NATO membership remaining steady at 20-30 percent, the war caused a surge in those in favour to more than 60 percent, according to opinion polls.

Public statements gathered by Finnish media suggest half of the 200 MPs now support membership, with only 12 opposing it. Others say they will announce a position after detailed discussions.

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

On Saturday, Finland’s European Affairs Minister Tytti Tuppurainen said she believed a Finnish application was "highly likely”.

"But the decision is not yet made,” she told Britain’s Sky News.

However, the Finns "seem to have already made up their mind and there is a huge majority for the NATO membership”.

Many analysts predict Finland could submit a bid in time for a NATO summit in June. Any membership applications 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 NATO chief Jens Stoltenberg that the alliance’s door remains open, and support from several members.

But Dmitry Medvedev, deputy chairman of Russia’s Security Council, said last weekthat should Sweden and Finland join NATO, then Russia would have to strengthen its land, naval and air forces in the Baltic Sea.

Medvedev also explicitly raised the nuclear threat by saying that there could be no more talk of a "nuclear-free” Baltic – where Russia has its Kaliningrad exclave sandwiched between Poland and Lithuania.

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

Finland declared independence in 1917 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.

The Nordic nation remained neutral during the Cold War in exchange for Soviet guarantees not to invade.

After the fall of the Iron Curtain, Finland firmly aligned itself with the West, by joining the EU and becoming a close partner of NATO.

Successive Finnish leaders shied away from full membership believing that military non-alignment was the best way to maintain working relations with the Kremlin.

Neighbouring Sweden is also considering its neutral position. A growing majority of Swedes are now in favour of joining NATO, a poll showed on Wednesday.

Sweden has not been at war since the time of Napoleon and has built its security policy on "non-participation in military alliances”. But like Finland, the February 24 invasion of Ukraine, which Moscow calls a "special military operation”, has forced a radical rethink.