STORY: Finland must join the NATO military alliance "without delay", the country's president and prime minister confirmed on Thursday (May 12).
In a major policy shift for the country - triggered by Russia's invasion of Ukraine.
Moscow said the move was "definitely" a threat and that it was ready to respond.
Having long warned Finland of consequences should it choose to join NATO, the Kremlin added that the expansion of the military bloc would not make Europe or the world more stable.
But Finland's neighbor Sweden is also close to a decision on asking to join NATO after decades of following a neutral path.
The announcement represents a huge setback for Russia, which had partly attempted to justify its invasion of Ukraine as a means to protect itself from NATO's eastwards expansion.
The Finnish parliament will debate the announcement on Monday (May 16).
Foreign minister Pekka Haaviston told EU lawmakers the move would improve security in the Baltic Sea region.
"Russia's invasion of Ukraine has altered the European and Finnish security environment. However, Finland is not facing an immediate military threat."
Kremlin spokesman Dmitry Peskov told reporters that Russia wanted to avoid a direct a clash with NATO.
But that Moscow was prepared to make a "decisive response" to anyone that tried to hinder Russia's "special military operation" in Ukraine.
Finland shares an 810 mile border with Russia that would more than double the current frontier between the U.S.-led alliance and Russia.
And put NATO guards a few hours' drive from the northern outskirts of St Petersburg.
Finland has gradually stepped up its cooperation with the North Atlantic Treaty Organization since Russia annexed Crimea in 2014.
But it had resisted joining NATO in order to maintain friendly relations with its eastern neighbor - until Russia's invasion of Ukraine in February .
Ahead of Thursday's joint statement Finnish President Sauli Niinisto said its move to join NATO deomstrated that Russia’s actions had backed it into a corner.
"If that would be the case, if we join, my response would be that you caused this. Look at the mirror."