Finland joins NATO, Russia threatens 'counter-measures'

Finland formally joined the NATO military alliance on Tuesday in a historic policy shift brought on by Russia's invasion of Ukraine, drawing a threat from Moscow of "countermeasures".

Finland's accession roughly doubles the length of the border that NATO shares with Russia and bolsters its eastern flank as the war in Ukraine grinds on with no resolution in sight.

Finnish Foreign Minister Pekka Haavisto completed the accession process by handing over an official document to U.S. Secretary of State Antony Blinken at NATO headquarters in Brussels.

"We welcome Finland to the alliance," NATO Secretary General Jens Stoltenberg said at the end of the brief ceremony.

Earlier, Stoltenberg had noted that Russian President Vladimir Putin had cited opposing NATO's eastward expansion as one justification for his invasion.