Finnish leaders on Thursday announced their support for Finland to join the NATO military alliance amid rising public support for NATO membership following the start of the Russia-Ukraine conflict. 

In a joint statement, Finland's President Sauli Niinisto and Prime Minister Sanna Marin said, "Finland must apply for NATO membership without delay." 

"NATO membership would strengthen Finland's security. As a member of NATO, Finland would strengthen the entire defense alliance," the statement reads.  

"We hope that the national steps still needed to make this decision will be taken rapidly within the next few days," the leaders said. 

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Finnish Foreign Minister Pekka Haavisto said on Tuesday that Finland would be ready to apply to join NATO after a few more steps. 

"When all our political parties are ready – and the latest, the Social Democrats on Saturday – then we are ready to move as [a] government forward and then this discussion, of course, on the NATO membership, will come to the Parliament, starting probably next Monday. But then we are, after that, ready to send an application," Haavisto said in an interview with CNBC. 

The foreign minister said earlier that Russia's military action in Ukraine had changed Finland's security situation, but added that there was no immediate threat. 

Russia launched what is describes as a "special military operation" in Ukraine on February 24. 

Finland, which has long adhered to a policy of military non-alignment and neutrality, shares a 1,340 kilometer border with Russia.

Finnish public support for joining NATO was for years at around 20-25 percent. But since the start of the Russia-Ukraine conflict, it has shot up to a record high of 76 percent, according to the latest opinion poll conducted by Yle, a major Finnish media company. 

Meanwhile, Finland's Scandinavian neighbor Sweden is also expected to make a decision on applying for NATO membership in the coming days.

Kremlin spokesperson Dmitry Peskov said on Thursday that Finland's entry into NATO would be a threat to Russia, according to TASS News Agency. He stressed that NATO's expansion does not contribute to security in Eurasia. 

The Russian Foreign Ministry said the Finnish leadership's statement in favor of the country's accession to NATO is a radical change in Helsinki's foreign policy. 

Russia will respond "according to the situation" to Finland's possible entry into NATO, the ministry stressed. 

Last month Russia warned of unspecified "consequences" should Finland and Sweden join NATO.  

"The choice is up to the authorities of Sweden and Finland. But they should understand the consequences of such a step for our bilateral relations and the architecture of European security as a whole," Russian Foreign Ministry spokeswoman Maria Zakharova said in a statement.

NATO Secretary General Jens Stoltenberg on Thursday welcomed the decision by Finland's leaders to favor joining the alliance. 

"Should Finland decide to apply, they would be warmly welcomed into NATO, and the accession process would be smooth and swift," Stoltenberg said. 

Pentagon spokesman John Kirby told MSNBC on Thursday that Finland's entry into NATO would be historic, adding it would not be difficult to integrate the country into the military alliance. 

Finnish President Niinisto and British Prime Minister Boris Johnson signed a joint statement pledging mutual assistance on Wednesday evening during Johnson's visit to Helsinki. Earlier in the day, Johnson signed a similar document with Swedish Prime Minister Magdalena Andersson in Harpsund, Sweden.