Donald Trump his taken his stand-off with North Korea to a new pitch by calling Kim Jong-un "a madman" and saying the Pyongyang leader "will be tested like never before."
Trump made the comments on Twitter after North Korea threatened to conduct a new test of a hydrogen bomb in response to new US sanctions.
The US President wrote: "Kim Jong Un of North Korea, who is obviously a madman who doesn't mind starving or killing his people, will be tested like never before!"
North Korea's earlier threat was made to reporters by Ri Yong-ho, the North Korean Foreign Minister, at the United Nations.
Ri told reporters that such a launch was at the discretion of the country's leader, Kim Jong-un.
It came in the wake of the US widening the existing economic sanctions against the regime in Pyongyang on Thursday.
Donald Trump's push to punish companies which trade with North Korea is the latest move to starve the regime of its resources in order to coerce it to back down on its nuclear programme.
The US president announced the decision shortly after meeting representatives from Japan and South Korea, which lie in North Korea's immediate range.
This was met with an infuriated response from Kim Jong-un, who called Trump a "deranged" rogue and a "gangster fond of playing with fire."
He insisted the US President would "pay dearly" if America launched an attack on North Korea.