'The DPRK regime's actions will continue to be grossly overmatched by ours and would lose any arms race or conflict it initiates.'
His comments come amid fears the crisis over North Korea could spiral in to global war after Donald Trump and Kim Jong-un made unprecedented threats to trade devastating missile strikes.
President Trump tweeted that America's nuclear arsenal is 'far stronger and more powerful than ever before', adding: 'There will never be a time that we are not the most powerful nation in the world!'
His remarks came after Pyongyang's volatile dictator warned he was 'carefully examining' plans to make 'an enveloping fire' around the US island of Guam, which is home to about 163,000 people and a sprawling American military base.
President Trump earlier made an apocalyptic warning that North Korea faces 'fire and fury like the world has never seen' over its nuclear program.