The Swedish move was spurred by Russia's invasion of Ukraine and turned the page on two centuries of non-alignment.

"Today, it is important to note that one more country in Europe has become more protected from Russian evil," Zelensky said in his evening address.

Russia has vowed "countermeasures" over Sweden's entry into NATO, especially if the alliance's troops and assets deploy in the country.

"At a time of Russian aggression... everyone sees how important it is to maintain alliances and partnerships," Zelensky added.

He has been pushing allies for a timetable to join the NATO ranks once the Russian invasion has been defeated.

Leaders have agreed that Ukraine could join the alliance once peace has been restored, but insisted certain conditions should be met.

"There will be a day when Sweden will be able to congratulate Ukraine on joining the alliance as well," Zelensky said.