"This is a historic moment, which we must seize," NATO Secretary-General Jens Stoltenberg said at a short ceremony, alongside the Swedish and Finnish ambassadors, amid Russia's invasion of Ukraine.
"I warmly welcome requests by Finland and Sweden to join NATO," he added, as quoted by the Reuters news agency. "You are our closest partners, and your membership in NATO will increase our shared security."
Amid the war in Ukraine, the accession process is expected to take only a few weeks, Reuters reported.
Poland's political leaders have voiced support for Sweden and Finland in their bids to join the 30-member Western military alliance.
"Poland welcomes the Finnish and Swedish governments’ decision to apply for North Atlantic Treaty Organisation membership," the Polish foreign ministry said in a statement on Tuesday.
"This historic step confirms the radical change in the security situation in Europe as a result of Russia's aggression against Ukraine," it added.
"Poland is convinced that Finland’s and Sweden’s NATO membership will strengthen security in the Baltic Sea region and contribute to extending the zone of stability in Europe," the Polish foreign ministry also said.
Source: IAR, PAP, Reuters, gov.pl