Finland’s prime minister and president on Thursday announced their intention to see their country—which has an 830-mile border with Russia—join the defensive pact. Sweden, which has an even longer history of neutrality than Finland does but no Russian border, is expected to make the same decision in the coming days.

“NATO membership would strengthen Finland’s security,” said Prime Minister Sanna Marin and President Sauli Niinistö in a highly anticipated joint statement. “As a member of NATO, Finland would strengthen the entire defense alliance. Finland must apply for NATO membership without delay.”

Also on Thursday, Sweden’s Expressen reported that the ruling Social Democrats there would on Sunday probably decide to make a Swedish application for NATO membership, with a formal decision following on Monday.

Marin is also a Social Democrat, and her party and its coalition partners will need to give their blessing on the weekend, to be followed by parliamentary approval that is expected next week.

Also on Thursday, the Finnish state-owned power-plant operator Fortum announced it was making a “controlled exit from the Russian market.” The company had already announced an investment and financing freeze in the country, but may now sell off its Russian operations entirely.

Kremlin spokesperson Dmitry Peskov reacted to Finland’s prospective NATO membership by saying it was “definitely” a threat to Russia.

Both Finland and Sweden have were largely happy staying out of NATO before Russia’s Ukraine invasion in late February. The former country has been neutral for eight decades, having chosen after two World War II–era Soviet invasions to sit out the subsequent Cold War. Sweden has been militarily nonaligned since the Napoleonic Wars.

In Finland, support for NATO accession was little more than 20% last year. By February, as Russia began signaling its coming offensive against Ukraine, it was up to 53%. This week it hit 76%. Separate polling published Thursday suggested that Finns were evenly split on the question of whether the country could defend itself in the event of a Russian attack.

In Sweden, polling showed in late April that 57% supported joining NATO, up from just a third in early 2021.

The big question now is how Russia will respond to the Nordic countries’ NATO accession, particularly in the months that likely lie between now and the applications being formally approved—all 30 existing NATO members need to give the green light, but NATO Secretary General Jens Stoltenberg said Thursday that Finland “would be warmly welcomed” into the club.

The U.K., which has been one of the most hawkish Western countries in the current crisis, has already moved to bridge the gap. Even though Finland and Sweden would be unable to activate NATO’s mutual-defense mechanism before joining the organization, British Prime Minister Boris Johnson on Wednesday agreed to defense deals with both countries, promising military support if anyone were to attack them.

Mikhail Ulyanov, a top Russian diplomat who liaises with international organizations in Austria, tweeted Thursday that Finland’s and Sweden’s likely NATO applications were “their choice.”

“The question is why they believe that their security will be strengthened,” he continued. “For example, if they join the Alliance they will need to subscribe to NATO’s de-facto proclamation of Russia as an adversary. How will subregional security benefit from that?”

Meanwhile, former Russian President Dmitry Medvedev warned Thursday that NATO countries’ continuing flow of weaponry to Ukraine “increase[s] the likelihood of a direct and open conflict between NATO and Russia,” and “such a conflict always has the risk of turning into a full-fledged nuclear war.”

Medvedev said last month that Finnish or Swedish accession to NATO would prompt Russia to move nuclear weapons to the region.