Finnish Prime Minister Sanna Marin says her country will decide whether to apply to join NATO "within weeks". She said she saw no reason to delay the decision, at a joint press conference alongside the Swedish prime minister.
Her comments coincided with a report in the Finnish parliament that said membership of the bloc could result in "increased tensions at the border between Finland and Russia".
Moscow has warned Finland and Sweden against NATO membership in recent weeks.
Finland and Sweden are militarily neutral, but Russia's invasion of Ukraine has spurred increased public support to become members of the Western defence alliance. Swedish leader Magdalena Andersson told reporters that the same "very serious analysis" was happening as in Finland and she saw no reason to delay it.
Swedish newspaper Svenska Dagbladet reported Wednesday that Andersson intended to apply for membership in time for the NATO summit in late June.
Finland shares a 1,340km border with Russia, and Kremlin spokesman Dmitry Peskov has stressed that Moscow will have to "rebalance the situation" with its measures if the NATO bid goes ahead.
"I'm not going to give any kind of timetable when we make our decisions, but I think it's going to happen soon enough," Ms Marin said. She noted that NATO membership offers Finland the security guarantee of Article 5, where an attack on a member is seen as an attack on all.
As the two Prime Ministers met in Stockholm, Finland's security review was beginning in Helsinki. Foreign Minister Pekka Haavisto said Russia's war has changed Europe's security environment and forced the revision of Finnish defence policy.