Donald Trump warned North Korea it will be "tested like never before" in an early-morning tweet.
It is the latest round in the ongoing war of words between Trump and Pyongyang over North Korea's nuclear weapons development.
In his tweet, Trump said: "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."
Kim Jong-un, in a rare personal statement on Friday 22 September, said: "I will surely and definitely tame the mentally deranged US dotard with fire. Action is the best option in treating the dotard who, hard of hearing, is uttering only what he wanted to say."
This came just days after Trump threatened to "totally destroy" North Korea if it continued with its nuclear weapons development.
Meanwhile, countries in the Pacific region near to North Korea are on high alert after Pyongyang warned it was considering a huge nuclear test somewhere in the area.
After a fierce war of words between Kim Jong-un and Donald Trump, the hermit nation brushed off any threat of sanctions and military action with the announcement they are considering testing "an unprecedented scale hydrogen bomb".
Any test would be illegal under international law. If a test was carried out, it would almost certainly be happen over a patch of international waters and at little or short notice.
It would give North Korea's opponents little opportunity to intercept or prevent the ICBM, unless the missile was aimed at waters or land around Japan, Guam or the mainland US, all stated targets of the regime.