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 news conference alongside Sweden’s prime minister.
Her comments coincided with a report to the Finnish parliament that said membership of the bloc could result in “increased tensions on the border between Finland and Russia”.
Moscow has warned Finland and Sweden against joining Nato in recent weeks.
Finland and Sweden are militarily non-aligned but Russia’s invasion of Ukraine has prompted increasing public support to become members of the Western defensive alliance. Swedish leader Magdalena Andersson told reporters that the same “very serious analysis” was taking place as in Finland and she saw no point in delaying it.
Swedish newspaper Svenska Dagbladet reported on Wednesday that Ms Andersson was aiming to apply for membership in time for a Nato summit in late June.
Finland shares a 1,340km (830 miles) border with Russia, and Kremlin spokesman Dmitry Peskov has stressed that Moscow would have to “rebalance the situation” with its own measures if the Nato bid went ahead.
“I won’t give any kind of timetable when we will make our decisions, but I think it will happen quite fast,” said Ms Marin. She pointed out that Nato membership offered Finland the security guarantee of Article Five, whereby an attack on one member is viewed as an attack on all.
While the two leaders met in Stockholm, Finland’s security review was being launched in Helsinki. Foreign Minister Pekka Haavisto said Russia’s war had changed the security environment in Europe and forced the review of Finnish defence policy.
Russia’s invasion of Ukraine is transforming European security. The Nato military alliance has been given new purpose and now – potentially – could get new members too.
Voters in Finland and Sweden have long cherished their non-aligned status. But now the mood is changing. Sanna Marin’s predecessor as prime minister, Alexander Stubb, says the decision is a “foregone conclusion”.
Sweden is also looking afresh at Nato – the country’s ruling Social Democrat party is reviewing its historic opposition to joining the alliance.
But Russian spokesmen have repeatedly said any expansion of Nato would be considered a “provocation” and warned there would be “consequences”.