Sweden and Finland need each of NATO's 30 members to approve their applications. The ratification process had been expected to take up to a year, though Turkey's objections have thrown that into doubt.
The Nordic countries, who had long adhered to a policy of neutrality and military non-alignment, made the dramatic change after the start of the Russia-Ukraine conflict.
Russian President Vladimir Putin said on Monday that the probable accession of Sweden and Finland to NATO poses "no immediate threat" to Russia, but warned against the expansion of NATO's military infrastructure into these countries. Russia and Finland share an over 1,300-kilometer land border.
"As to enlargement, Russia has no problem with these states – none. And so in this sense there is no immediate threat to Russia from an expansion (of NATO) to include these countries," Putin told the leaders from the member countries of the Collective Security Treaty Organization in Moscow.
"But the expansion of military infrastructure into this territory would certainly provoke our response," he said.