Finland will almost certainly apply for membership in NATO, Sweden's Foreign Minister Ann Linde told Swedish television on Sunday.

Russia's invasion of Ukraine has forced both Sweden and its eastern neighbour Finland to review beliefs that military neutrality is the best means of ensuring national security.

"We know more or less that they (Finland) will apply for NATO membership. And that changes the whole balance. If one of our countries joins, we know that tensions would increase," Linde told public broadcaster SVT.

Asked whether she thinks Finland will join NATO, Linde said:

"I think you can say that quite surely."

Both Sweden and Finland are expected to decide on whether to join the military alliance in the coming weeks. Finland's Foreign Minister Pekka Haavisto said on Friday that he hoped Finland and Sweden would make similar decisions at the same time.