DONALD Trump warned the US is poised to unleash the full force of its military power to defend against the "worldwide threat" from North Korea.

The US President took a tough stance during his visit to South Korea today, saying tyrant Kim Jong-un is threatening "millions" of lives.

Donald Trump warned the US is poised to unleash the full force of its military power to defend against North Korea

He called on world powers, particularly China and Russia, to act with "urgency and great determination" to put more pressure on the North.

"We cannot allow North Korea to threaten all that we have built," Trump told the press conference on the first day of his visit on Kim's doorstep.

"North Korea is a worldwide threat that requires a worldwide action."

Trump made it clear that the US was fully prepared to wield the "full range" of America's arsenal, but added: "We hope to God we don't have to".