In a joint statement released this morning, Prime Minister Sanna Marin and President Sauli Niinistö said Finland must apply for NATO membership without delay.
The announcement was widely expected and has broad support in the country: A recent poll showed that about three-quarters of all Finns support joining the military alliance.
The invasion of Ukraine in February prompted Finland, which shares an 830-mile border with Russia, to move away from its long history of neutrality and military nonalignment.
Finland's neighbor Sweden also is considering joining NATO. Moscow has warned both countries against joining.
On Thursday, Kremlin spokesperson Dmitry Peskov called Finland's entry into NATO a threat to Russia and said it "does not make our continent more stable and safe."
Russia's reaction will depend on what the expansion process looks like and how close NATO's military infrastructure gets to Russia's borders, he said, adding that Russia will analyze events and take measures to "keep the situation in balance and maintain our security."
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This story originally appeared in the Morning Edition live blog.