US Defence Secretary General James Mattis said dictator Kim Jong-un would never be allowed to achieve his goal of becoming a nuclear power.
He told reporters the US goal was the “denuclearisation” of the hermit dictatorship as he condemned Kim’s aggressive rhetoric.
General Mattis told reporters: “I cannot imagine a condition under which the US can accept North Korea as a nuclear power.”
He said: “Any North Korean aggression or military provocation will not be tolerated”, as he warned that provocative nuclear testing would not endear the secretive nation to the international community.”
General Mattis spoke during his week-long trip to Asia to stress that the US would prefer to pursue diplomatic solutions to tensions with North Korea.
He attended top-level military talks in Seoul on Saturday alongside South Korean defence secretary Song Young-moo.
Both defence chiefs condemned the North’s nuclear provocations in the wake of Kim’s six missile tests in rapid succession.
General Mattis also warned of a “massive military response” if North Korea launches a nuclear attack.
He said North Korea’s military was no match for the US-South Korean alliance and that diplomacy was most effective “when backed by credible military force”.
The Defence Secretary said: “Make no mistake – any attack on the United States, or our allies, will be defeated.
“And any use of nuclear weapons will be met with a massive military response that is both effective and overwhelming.”
General Mattis’ comments follow months of escalating tensions between the US and Pyongyang following the series of missile tests.
The two countries have threatened to obliterate each other while Kim has pledged to build a nuclear missile that can reach the United States.
The CIA has warned North Korea could be only months away from developing the ability to reach the United States with nuclear weapons.
President Donald Trump, who has threatened to destroy North Korea if necessary, is heading to Asia this week, with his trip including a stop in South Korea to meet President Moon Jae-in.