Finland joins NATO as Russia threatens countermeasures

Finland formally joined NATO on Tuesday, more than doubling the length of the military alliance's border with Russia and drawing a threat of countermeasures from the Kremlin.

"This will make Finland safer and NATO stronger," the alliance's Secretary General Jens Stoltenberg said. 

Finland became the 31st member of NATO after Turkey initially opposed the country's application.

All alliance members must approve new applicants, and Turkey's holdout is still preventing Sweden from joining after the two Nordic nations applied to NATO last year.

After Finland joined the alliance, Russian Press Secretary Dmitry Peskov said, "NATO expansion is forcing Russia to take countermeasures to ensure its own security, both tactically and strategically.

"Moscow will closely monitor what will happen in Finland after joining the alliance - based on this, the measures it considers necessary will be taken," according to Russian-state outlet RIA, as translated.

Because Finland shares a more than 800-mile border with Russia, its addition to the alliance more than doubles Russia's border with NATO nations. The Kremlin threatened last year to take nuclear measures if Finland joined NATO.