"The views of citizens are certainly changing and I believe those of the parties and their members are also changing," due to the deteriorating security environment, Marin said.

She was speaking to reporters after party leaders met to consider how to respond to a public petition calling for a referendum on NATO membership.

But she cautioned against "drawing conclusions", saying: "We will evaluate the right way to proceed."

The Nordic country of 5.5 million shares a 1,340 kilometre (830 mile) border with Russia and, despite joining the EU in 1995, has remained outside the military alliance, in large part for fear of reprisals from Moscow.

Yet support for becoming a NATO member, which would see Finland benefit from the alliance's mutual defence clause, has reached an all-time high since Russia began its assault on Ukraine last Thursday.

For the first time, a majority (53 percent) of Finns are in favour of joining the Atlantic alliance, according to a poll published on Monday by public broadcaster Yle.

One month ago a survey in the Helsingin Sanomat newspaper put support for NATO membership at just 28 percent.

"This debate is underway, it is intensifying and it is certain to gather pace," Marin said on Tuesday.

In another "historic decision", Finland on Monday also agreed to send weapons to Ukraine, including 2,500 assault rifles, ammunition and 1,500 single-use anti-tank weapons.

Experts expect Finland to act in concert with Sweden, which is also weighing whether to join NATO.

Such a move would further heighten tensions between Russia and the West, since the eastward expansion of NATO is the prime security grievance for 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.