• Finland is not alone in reconsidering its security policy.
• Neighboring Sweden has also been reviewing its stance in the aftermath of Russia's aggression in Ukraine.
• Before both countries join the defense alliance, the 30 members already in NATO will have to approve their applications.
• That process is likely to take at least some months.

HELSINKI, Finland — After completing a few more steps, Finland will be ready to send its application to join the NATO military alliance, the country's foreign affairs minister told CNBC Tuesday.

The Nordic nation has been considering joining the alliance in the wake of Russia's unprovoked invasion of Ukraine. Finland's Prime Minister Sanna Marin has previously said the invasion "changed the security policy situation in such a way that there is no going back to the way things were."

Joining NATO would mark a sharp U-turn in Finland's decades-long policy of neutrality but could lead to a backlash from Russia, where President Vladimir Putin has been vocal about his opposition to NATO enlargement.

"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," Pekka Haavisto, Finland's minister for foreign affairs, said.

Finland is currently led by a five-party coalition government. Finnish president, Sauli Niinisto, is due to announce his opinion on the country's membership of NATO Thursday, kicking off a sequence of events that should result in the formal application being sent through.

But Finland is not alone in reconsidering its security policy. Neighboring Sweden has also been reviewing its stance in the aftermath of Russia's onslaught in Ukraine.

"I've been really much in favor of us [Finland and Sweden] joining together and now it looks like we have a parallel process, which could end in a similar way," Haavisto told CNBC, adding that Sweden is likely to send its NATO application "around the same time" as Finland.

"We have very good cooperation on military issues with Sweden, actually, we can have a common surveillance of our airspace, on our maritime areas and so forth, and we are relying very much [on] each other, and of course, if it so happens in the future that one is in the ... defense alliance and the other one is not — that might hamper also our good cooperation," he said about the reasoning behind applying at the same time.

Several NATO members, notably Germany and the United States, have said they are ready to provide security guarantees to Stockholm and Helsinki during the period of time between their applications and official membership.

Before both countries join the defense alliance, the 30 members already in NATO have to approve their applications. A process that is likely to take at least some months.

NATO Secretary General Jens Stoltenberg has spoken about a "minimum delay" for their applications.

June NATO summit

In the meantime, Finland is hoping to receive some political commitments from the alliance at a summit in June, due to take place in Madrid, Spain.

"Madrid is very important for political commitments and, on the highest level, welcoming new member states like Finland and Sweden," Haavisto said.

"But even prior to that, the NATO Council certainly will discuss this matter and we are also expecting that single NATO member states will give their commitments and opinions immediately when Finland and Sweden will send an application," he added.