Finland wants to join the North Atlantic Treaty Organisation (NATO) as soon as possible.
Finland's President and Prime Minister revealed they want their country to join the NATO military alliance 'without delay', with Sweden also expected to follow suit.
Joining the alliance will strengthen Western ties, bringing NATO right up to Russia's border as Moscow continues its assault on neighbouring Ukraine.
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The Kremlin described Finland's bid to join NATO as a hostile move that 'definitely' poses a threat to Russian security.
The Russian Foreign Ministry has described it as ‘a radical change in the country's foreign policy’.
"Finland's accession to NATO will cause serious damage to bilateral Russian-Finnish relations and the maintaining of stability and security in the Northern European region," it said in a statement.
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"Russia will be forced to take retaliatory steps, both of a military-technical and other nature, in order to neutralise the threats to its national security that arise from this."
The Kremlin, however, did not spell out what retaliation would look like.
Kremlin spokesman Dmitry Peskov said that Finland's NATO bid does not make Russia 'more stable and secure'.
"Finland joined the unfriendly steps taken by the European Union towards our country," Peskov said.
When asked to expand on Russian retaliation, he added: "Everything will depend on how this [NATO] expansion process plays out, the extent to which military infrastructure moves closer to our borders."
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In a joint statement, Finnish President Sauli Niinistö and Prime Minister Sanna Marin said: "NATO membership would strengthen Finland’s security. As a member of NATO, Finland would strengthen the entire defence alliance."
Niinistö confirmed that his desire to have his nation join the Western alliance came down to Russia's decision to invade Ukraine.
"Joining NATO would not be against anyone," he said, according to the BBC.
He then said to Russia: "You caused this. Look in the mirror."
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Finland shares a 1,300 kilometre border with Russia and has previously opted not to join NATO to steer clear of aggravating its neighbour to the east.
Finland and Sweden are expected to announce their final decisions to join NATO on Sunday (May 15).
NATO Secretary General Jens Stoltenberg said he expects the process of giving membership to Finland and Sweden to occur 'quite quickly', the BBC reports.