North Korean leader Kim Jong Un called Donald Trump "deranged" and said in a statement carried by the state news agency that he will "pay dearly" for his threats.
He said that Trump is "unfit to hold the prerogative of supreme command of a country" and described the president as "a rogue and a gangster fond of playing with fire".
"I will make the man holding the prerogative of the supreme command in the US pay dearly for his speech calling for totally destroying the DPRK," said the statement carried by the Korean Central News Agency in a dispatch issued from Pyongyang on Friday morning.
DPRK is the abbreviation of the communist country's official name, the Democratic People's Republic of Korea.
The statement responded to Trump's combative speech at the UN General Assembly on Tuesday where he mocked Kim as a "rocket man" on a "suicide mission" and said that if "forced to defend itself or its allies, we will have no choice but to totally destroy North Korea".
Kim Jong Un described Trump's comments as "mentally deranged behaviour".
He said the remarks "have convinced me, rather than frightening or stopping me, that the path I chose is correct and that it is the one I have to follow to the last".
He added that he is "thinking hard" about his response and that Trump "will face results beyond his expectation".
In recent months, North Korea has launched a pair of intercontinental missiles believed capable of striking the continental United States and another pair that soared over Japanese territory.
Earlier this month, North Korea conducted its most powerful nuclear test to date, drawing stiffer UN sanctions.
AP