Finland's President and Prime Minister stated on Thursday that they are in favor of joining NATO, and a formal decision will be taken this weekend.

The Kremlin immediately responded to the announcement, saying Finnish membership in NATO was "definitely" a threat to Russia.

Neighbouring Sweden, which like Finland has been military non-aligned for decades, is also expected to announce its decision in the coming days, very likely at a meeting on Sunday of Prime Minister Magdalena Andersson's Social Democratic Party.

"Finland must apply for NATO membership without delay," President Sauli Niinisto and Prime Minister Sanna Marin stressed in a joint statement.

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

Russia warns of consequences

A special committee will announce Helsinki's formal decision on a membership bid on Sunday, it added.

Moscow has repeatedly warned Stockholm and Helsinki of the consequences if they were to join NATO.

Niinisto told reporters on Wednesday that "joining NATO would not be against anyone."

76% of Finns support joining NATO

In the same context, a poll published on Monday by public broadcaster Yle showed that a record 76% of Finns now support joining NATO, up from the steady 20-30% registered in recent years.

A country of 5.5 million people, Finland shares a 1,300-kilometer (800-mile) border with Russia.

Defence Minister Antti Kaikkonen pointed out Thursday a NATO bid would "significantly raise the threshold for Finland to be the target of a military attack."

"This is a defensive solution that threatens no one," he wrote on his blog.

Kaikkonen said he hoped Sweden would come to the same conclusion and "we could apply for membership together."

Swedish Foreign Minister Ann Linde told news agency TT that "Finland's decision is naturally of great importance to Sweden" and said her government would announce its decision "soon". 

European Council President Charles Michel wrote on Twitter that Finland joining NATO would "greatly contribute to European security. With Russia waging war in Ukraine it's a powerful signal of deterrence."

Finland could be NATO member "at the earliest" on Oct. 1

Finland and Sweden have long cooperated with NATO and are expected to be able to join the alliance quickly.

NATO Secretary-General Jens Stoltenberg said Thursday that Finland's entry would be "smooth and swift."

The next step is for Finland's President and Ministerial Committee on Foreign and Security Policy -- a body made up of the President, Prime Minister, and up to six other cabinet ministers -- to meet on Sunday.

The committee will make the formal decision on whether to submit a Finnish application.

The proposal will then be presented to parliament for a debate, which is expected to take place on Monday. 

After an official bid is submitted to the alliance, negotiations get underway. Lawmakers in all 30 NATO member states then need to ratify Finland's application, a process that can take months.

Foreign Minister Haavisto said on Tuesday he believed Finland could be a full NATO member "at the earliest" on October 1.

As candidate countries are not covered by NATO's Article 5 mutual defense agreement, both Finland and Sweden have sought assurances from NATO members that they would be protected while awaiting full membership.