"With Sweden and Finland, we don't have the problems that we have with Ukraine. They want to join NATO, go ahead," Putin told Russian state television on Wednesday after talks with regional leaders in Turkmenistan.
"But they must understand there was no threat before, while now, if military contingents and infrastructure are deployed there, we will have to respond in kind and create the same threats for the territories from which threats towards us are created."
He said it was inevitable that Moscow's relations with Helsinki and Stockholm would sour over their NATO membership.
"Everything was fine between us, but now there might be some tensions, there certainly will," he said.
"It's inevitable if there is a threat to us."
Putin made his comment a day after NATO member Turkey lifted its veto over the bid by Finland and Sweden to join the alliance after the three nations agreed to protect each other's security.
The move means Helsinki and Stockholm can proceed with their application to join NATO, marking the biggest shift in European security in decades.
Putin said the objectives of Moscow's "special military operation" in Ukraine remained unchanged, that its goal was to "liberate" eastern Ukraine's Donbas region and create conditions to ensure Russia's security.
He said Russian troops had advanced in Ukraine and the military intervention was going as planned.
There was no need, he said, to set a deadline for an end to the campaign.
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