According to sources knowledgeable about the situation, Sweden and Finland have decided to submit joint admission applications to the US-led NATO alliance as soon as the middle of next month.

Stockholm had proposed on Monday that the two countries express their desire to join on the same day, and Helsinki had accepted as long as the Swedish administration had made its selection.

In spite of the tightening coordination with the military alliance since Moscow's 2014 annexation of Crimea, the Nordic countries have chosen to remain aloof. However, Russia's operation in Ukraine has prompted Sweden and Finland to reconsider whether their long-standing military neutrality is really the best way to ensure national security.

Sanna Marin, prime minister of Finland, stated at the time that Finland, which shares an 810-mile border with Russia, would make a decision "very quickly, in weeks not months," despite the risk of offending Moscow.

Magdalena Andersson, her Swedish counterpart, said that her country had to be ready for all kinds of Russian acts and that everything had shifted when the Kremlin attacked Ukraine.  Russia has forewarned both nations against the action on numerous occasions.

If Finland and Sweden choose to leave years of military non-alignment by joining NATO, Russia said it would be compelled to restore military balance by boosting its Baltic defenses, even by installing nuclear weapons.

Sweden's foreign minister, Ann Linde, announced last week that a wide-ranging security policy assessment would be completed by May 13 instead of May 31 as anticipated, adding that there is now a lot of pressure because Finland's assessment has already been released.

The simultaneous applications could be made in the week of May 16th, coinciding with Finnish President Sauli Niinistö's state visit to Stockholm. 

According to the latest opinion polls, 68% of Finns support entering the alliance, which is more than double the percentage before the war, with only 12% against it. According to polling in Sweden, a tiny majority of the people also support joining.

Finland and Sweden are officially nonaligned militarily, but after renouncing their prior policy of strict neutrality when they joined the EU in 1995 after the conclusion of the cold war, they became NATO collaborators, participating in drills and sharing intel.

The leaders of both countries set an appointment in the week of May 16th and would then openly state their intentions to join the alliance.