North Korean leader Kim Jong-un called Donald Trump "mentally deranged" in a statement carried by the state news agency Thursday (21 September) saying the US president will "pay dearly" for his fiery threats at the UN General Assembly.

"The mentally deranged behavior of the U.S. president openly expressing on the U.N. arena the unethical will to 'totally destroy' a sovereign state, beyond the boundary of threats of regime change or overturn of social system, makes even those with normal thinking think about discretion and composure," Kim said in statement carried by North Korea's official Korean Central News Agency.

Kim also urged Trump to "exercise prudence in selecting words", adding that the president's 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".

The Pyongyang leader's escalating remarks come after Trump delivered a stark warning during his maiden speech at the UN in which he threatened to "totally destroy" North Korea if it attacked the US or its allies. He also referred to the North Korean leader as a "Rocket Man" on a "suicide mission".

Over the past few weeks, North Korea conducted a number of intercontinental ballistic missile tests and sent two over Japanese airspace. The UN, in response, passed tighter sanctions on the hermit kingdom's ability to import crude oil and petrol.

On Thursday, Trump signed an executive order that expands US sanctions on North Korea to "cut off sources of revenue that fund North Korea's efforts to develop the deadliest weapons known to humankind".

Kim, however, defiantly described Trump as a "rogue and a gangster fond of playing with fire, rather than a politician" and said a "frightened dog barks louder".

"I will surely and definitely tame the mentally deranged US dotard with fire," he said.

In response to the escalating rhetoric between the two leaders, Twitter users urged the two leaders to deal with the issue themselves without nuclear weapons and "leave the rest of the world out of it." One Twitter user wrote: "This is what happens when you taunt a mad man."

Another said: "Nobody wins in this pissing contest."

While some Twitter users argued that the North Korean leader's description of Trump was "not wrong," others delved into his descriptive response and honed in on Kim's use of the word "Dotard."

Merriam-Webster tweeted that searches for the archaic word were "high as a kite," and shared a link to its definition. According to Merriam-Webster, a dotard describes a person in a state of "senile decay marked by decline of mental poise and alertness".

"I agree with the statement (without condoning NK behavior)," one person said. "Everyone's looking up 'dotard' and saying 'oh, yeah, that's bang on actually'."

Many people voiced their exasperation and fear over how Trump will respond to Kim's latest comments. One person warned: "Now would be a really good time to take Twitter away from Trump."

North Korea Guam strike threat
North Korean leader Kim Jong Un claps with military officers at the Command of the Strategic Force of the Korean People's Army (KPA) in an unknown location in North Korea in this undated photo released by North Korea's Korean Central News Agency KCNA via Reuters