North Korea says Donald Trump's labelling of Kim Jong-Un as "Rocket Man" has made "our rockets' visit to the entire U.S. mainland inevitable''.

Foreign Minister Ri Yong-ho told the United Nations that Mr Trump had committed an irreversible mistake during his speech to the body in New York last week.

His comments came after it emerged the US had sent bombers to the North Korean border today in the closest they have been this century.

Foreign Minister Ri said if US lives were lost, Mr Trump ''will be held totally responsible''.

Ri, who said Pyongyang's ultimate goal was to establish a "balance of power with the U.S.", retorted that Trump himself was on a "suicide mission" after the U.S. president said Kim was on such a mission.