In the joint statement, Niinisto and Marin said: “NATO membership would strengthen Finland’s security. As a member of NATO, Finland would strengthen the overall defense alliance. Finland must immediately apply for NATO membership. We hope that national steps are still required to make this decision will be made swiftly within the next few days.”
Later Thursday, Russia’s foreign ministry said the Finnish statement marked a “radical shift in the country’s foreign policy” and warned of countermeasures.
“Helsinki must be aware of the responsibility and the consequences of such a step,” the ministry said.
Finland’s possible entry into NATO would cause serious damage to bilateral Russian-Finnish ties that maintain stability and security in the northern European region, the ministry said.
“Russia will be forced to take both military-technical and other retaliatory measures to stop the threats to its national security arising in this regard,” it said.
Also on Thursday, Kremlin spokesman Dmitry Peskov said that Finland’s entry into the alliance would not improve security.
“As we have said many times, NATO enlargement does not make the world more stable and secure,” Peskov told reporters. He added that Russia’s response would depend on NATO activity near its borders.
“It will depend on what this expansion process entails, how far and how close the military infrastructure moves to our borders,” Peskow said.
The spokesman added that Russia will analyze the situation with Finland joining NATO and work out the necessary measures to ensure its own security.
Peskov also told reporters on a regular conference call, “Everyone wants to avoid a direct clash between Russia and NATO: both Russia and NATO, and most importantly Washington.” However, he added that Russia is ready to help those who would try to take part in the country’s “special military operation” in Ukraine – the Kremlin’s official description of Russia’s war there – to provide “the most decisive response”.
Since the Russian invasion of Ukraine in February, public support for Finland’s NATO entry has risen from around 30% to nearly 80% in some polls.
The move would require the approval of Finland’s parliament and the removal of other domestic legal hurdles, but NATO Secretary General Jens Stoltenberg said the country would be “warmly welcome” to the alliance if it applied for membership.
“I welcome the joint statement by President Niinisto and Prime Minister Marin, who support an immediate application for NATO membership,” Stoltenberg said on Thursday, according to his office.
“This is a sovereign decision by Finland, which NATO fully respects. Should Finland decide to apply, it would be warmly welcomed into NATO and the accession process would be smooth and swift. Finland is one of NATO’s closest partners, a mature democracy, a member of the European Union and an important contributor to Euro-Atlantic security,” he said.
The NATO chief said he agreed with Niinisto and Marin “that NATO membership would strengthen both NATO’s and Finland’s security.”
Sweden, Finland’s western neighbor, is also expected to soon announce its intention to join the alliance through a similar process.
Russia has previously warned both countries against joining NATO, saying there would be consequences.
European diplomats and security officials widely believe that Finland could quickly join the alliance once negotiations begin, given its decades-long purchase of military hardware compatible with its Western allies, including the US, and already meeting many of the criteria for membership Fulfills.
Finland joining NATO would have both practical and symbolic consequences for Russia and the western alliance.
Finland has been militarily non-aligned and nominally neutral since the end of World War II so as not to provoke Russia. It has at times given in to the Kremlin’s security concerns and tried to maintain good trade relations.
However, the war in Ukraine has sufficiently changed the calculus that NATO membership now appears to be the best path forward, regardless of how Russia might react to it.
European defense officials who have spoken to CNN over the past few months believe that NATO countries will offer some guarantees for Finland’s security during the accession process in case Russia retaliates before officially joining.
On Wednesday, British Prime Minister Boris Johnson announced new security pacts with Finland and Sweden, promising to come to the aid of both countries if either were attacked.
Finland has historically had high defense spending and still has a policy of conscription, requiring all adult males to be called up for military service. It is widely acknowledged among NATO officials that Finland’s entry into the alliance would provide a significant boost in the fight against Russian aggression, since the country has historically taken its own security very seriously.
It also shares a more than 800-mile border with Russia, which is significant because before invading Ukraine, the Kremlin said it wanted NATO to restore its borders to where they were in the 1990s.
Instead, President Vladimir Putin’s move could see a stronger NATO draw closer.
CNN’s Anna Chernova, Niamh Kennedy, Uliana Pavlova, Radina Gigova and James Frater contributed to this report.