Finland's leaders on Thursday said the country would apply to join NATO "without delay." 

"Finland must apply for NATO membership without delay," President Sauli Niinistö and Prime Minister Sanna Marin said in a joint statement. "We hope that the national steps still needed to make this decision will be taken rapidly within the next few days." 

Leaders in both Sweden and Finland had been expected to announce their positions on joining NATO this week, as the war in Ukraine continues to have unintended consequences for Russia by potentially pushing two more of its neighbors to the transatlantic alliance.

Finland’s decision to apply for NATO membership is a threat to the Kremlin, Dmitry Peskov, Russia's presidential press secretary, said on Thursday.

"Another enlargement of NATO does not make our continent more stable and secure,” Peskov told reporters.

Swedish Minister of Foreign Affairs Ann Linde said on Thursday that Finland's leaders had delivered an "important message," adding that her country "will decide after the report from the security policy consultations has been presented." Sweden's ruling party is expected to announce its position on May 15. Finland's parliament is expected to debate the issue and then vote a day later.

The Scandinavian countries have long held neutral status when it comes to European conflict. Finland became a neutral country after the Second World War, while Sweden has resisted military alliances long before that.

Yet fears that Russia could do to other non-NATO countries what it has done to Ukraine has sparked a rapid shift in public opinion in both countries, one of which, Finland, shares an 830-mile land border with Russia.

Both could be on the cusp of joining NATO. NATO Secretary-General Jens Stoltenberg has publicly said the Nordic countries would be welcomed into the alliance.

NATO's expansion would be yet another unintended consequence for Russia, as they continue to be met with fierce resistance in Ukraine and a more united West than their intelligence assessments anticipated. Part of Russia's security demands ahead of the invasion in Ukraine included reverting NATO forces to 1997 positions.