"In the midst of an acute crisis it is particularly important to keep a cool head and carefully assess the impact on our security" from the Ukraine crisis, President Sauli Niinisto said in a statement after meeting senior MPs and defence chiefs.

Russia's invasion of Ukraine has sparked a lively debate in Finland over whether the militarily non-aligned country should join NATO, with a recent poll showing majority support for membership for the first time.

Petitions in favour of a referendum on NATO membership have amassed tens of thousands of signatures in the last week, meaning the issue will be debated by MPs in parliament, the Eduskunta.

Finland, which shares a 1,300 kilometre (800 mile) border with Russia, remained neutral during the Cold War in exchange for assurances from Moscow that Soviet troops would not invade.

The Nordic country of 5.5 million people has since joined the EU and enjoys a close partnership with NATO, sharing intelligence and resources.

"Our security environment is now undergoing rapid and dramatic change," Niinisto said. "I fully understand the concern felt by Finns and the need to respond to the situation."

Experts expect Finland to act in concert with neighbouring Sweden on whether to join NATO.

If they did, it would further heighten tensions between Russia and the West, since the eastward expansion of the alliance is the prime security grievance of the Kremlin.

Last Friday, Russia's foreign ministry warned that if the Nordic countries were to join NATO it would "have serious military and political repercussions".

Helsinki shrugged this off as a warning it had heard before.