After 25 years of tranquil post Cold War relations, Finns are once again worried about the threat posed by their resurgent eastern neighbour Russia, though they remain firmly opposed to joining NATO.

The issue has been on everybody's lips since Russia annexed the Crimean peninsula from Ukraine last year, but despite the tangible concern, the question of NATO membership has been broadly avoided in political debates ahead of Sunday's legislative elections.

"Security is surprisingly absent in the election debates. Finns have discussed security issues quite intensively in the media, especially the conflict in Ukraine and Russia's behaviour, but (the issue has been) avoided in the debates," Helsinki University political history professor Juhana Aunesluoma told AFP.

"People are clearly concerned about it but they seem to stand behind the government consensus right now, which is to stick with EU policy to strengthen collaboration with NATO within existing agreements," he added.

"It's more like people think about it long-term. Maybe one day Finnish security policy will have to change but they don't see that a change would be imminent," Aunesluoma said.

The Nordic country of 5.5 million inhabitants shares a 1,340-kilometre (830-mile) border with Russia.

Finland's military non-alignment is seen as an important tool for maintaining good relations with its powerful neighbour.

The two countries waged a horrific war in 1939-1940, still fresh in the minds of Finland's oldest generation.

For decades during the Cold War, when it was strategically positioned between East and West, Finland's uncritical stance towards the Soviet Union allowed it to access a vast market while trading extensively with the West.

Helsinki has however aligned itself with the West after the fall of the Soviet Union, joining the EU in 1995 and inching closer to NATO.

It is part of NATO's Partnership for Peace programme, and has for example participated in the Alliance's ISAF operation in Afghanistan.

But Helsinki has prioritised EU-based military cooperation over NATO.

The head of the Finnish military, Commander Jarmo Lindberg, says Russia has done nothing that could be considered as posing an acute threat to Finland.

However, "the entire volume of activity near Finland's borders has grown. For this reason we need to re-examine our preparedness accordingly."

- 'Biggest challenge to European security' -

Finland and its Nordic neighbours say they have seen an uptick in Russian military activity over the last year, including several airspace violations and war planes allegedly flying without their identifying transponders.

Just last week, Finnish Defence Minister Carl Haglund joined his Nordic counterparts in issuing a declaration referring to Russia as the "biggest challenge to European security".

"The security situation around the Nordic countries has significantly worsened during the past year," the ministers wrote.

Finland, Sweden, Denmark, Norway and Iceland agreed to step up their military cooperation following the changed security situation, including more joint military exercises, intelligence exchanges and stronger defence industry ties.

"Russia's propaganda and political manoeuvering are contributing to sowing discord" within both the EU and NATO, they added.

The declaration prompted the Russian foreign ministry to express "concern" that non-NATO members Sweden and Finland were increasing their cooperation with NATO members Denmark, Norway and Iceland.

Finnish Prime Minister Alexander Stubb hastened to tell Finns they should not let Russia's "sabre-rattling" startle them, while Foreign Minister Erkki Tuomioja insisted Russia was not a threat.

But a poll published in Finnish broadsheet Helsingin Sanomat in March showed that 61 percent of Finns either completely or somewhat agreed with the statement that "Russia is now a greater threat to Finland".

At the same time, 57 percent of respondents said they were opposed to joining the North Atlantic Alliance, while 27 percent were in favour -- the highest support level recorded since 2002.

Despite the recent developments, Finland still "has a good, close working relationship with Russia," Aunesluoma said.

And that is not seen changing after Sunday's legislative election, in part because foreign and security policy is decided jointly between Finland's president and the government.

"It doesn't seem that there will be a big change. The current line has already been agreed between the big parties and the government and the president," Aunesluoma said.

After a three-year economic slump, voters are widely expected to oust the left-right coalition headed by conservative Prime Minister Stubb, in favour of the agrarian-liberal Centre Party.