"We will have very careful discussions but not taking any more time than we have to," the Social Democrat leader told a press conference.

"I think we will end the discussion before midsummer," she said.

Finland is not a member of NATO and is officially non-aligned, although it is a close partner of the military alliance, along with neighbouring Sweden, and a member of the EU.

Though Finns traditionally have been against NATO membership, there has been a dramatic jump in public and political support for joining in recent weeks following the February 24 start of the war in Ukraine.

Opinion polls have shown that nearly 60 percent of Finns are now in favour of membership, a doubling of the support before Russia's invasion.

The Finnish government is due to publish a report next week, on the new security situation in the Nordic country.

The report is expected to be a prelude to a national and parliamentary debate in the country of 5.5 million people, which shares a 1,340-kilometre (830-mile) long border with Russia.

A NATO summit is scheduled for June 29-30 in Madrid and Finnish Foreign Minister Pekka Haavisto acknowledged on Thursday that many NATO members had asked whether Helsinki intended to apply before then.

Finland has already announced a two-billion-euro increase in its defence budget by 2026, a hike of 40 percent.

The invasion of Ukraine has also put the question of NATO membership on the agenda in neighbouring Sweden, and analysts expect the Nordic neighbours to act in concert on whether to join NATO.

The eastward expansion of the alliance is a prime security grievance of the Kremlin and Russia has previously warned that if the Nordic countries join NATO it would "have serious military and political repercussions".