NATO warned it had the "capabilities and resolve to respond to any aggression" meted out by North Korea.
Jens Stoltenberg, the secretary general of the American and European defence group, "strongly condemned" Pyongyang's nuclear missile test programme in Seoul today (2 November).
In a speech to policy advisers in the South Korean capital the Norwegian said: "We have the capabilities and resolve to respond to any aggression. Our position is clear - North Korea must abandon its nuclear programme, once and for all."
Stoltenberg added the nuclear armament of the communist state led by Kim Jong-un was "a clear and present danger" to NATO's Asian partners South Korea and Japan.
He added: "North Korea is developing ballistic missiles capable of hitting cities both in North America and in Europe."
Stoltenberg warned that the communist regime "must refrain from further testing".
The secretary general's comments come after around 200 people are reported to have died when tunnels collapsed at a North Korean nuclear test site, it emerged this week.
The accident happened at the Punggye-ri underground nuclear test site in northeast North Korea on 10 October.
The previous month the regime exploded a nuclear bomb at the underground site, setting off an earthquake with a magnitude of about 6.3 that was felt as far away as China.
It was Pyongyang's sixth nuclear weapons test in 11 years, although the last three have come within the last 12 months.
The acceleration of North Korea's missile programme has destabilised the east Asian region and led to a furious war of words, that hint at a nuclear exchange, between Kim Jong-un and US President Donald Trump.