The exchange of insults followed Trump's announcement of ramped up economic sanctions on North Korea and comes after a United Nations speech Tuesday in which Trump responded to Kim's buildup of nuclear and ballistic missile capabilities by calling him "rocket man" who is on a "suicide mission".
CHANG: Kim lectured the USA president, calling his behavior mentally deranged.
Ri Yong Ho called the American president "a mentally deranged person full of megalomania and complacency" with his finger on the "nuclear button".
He added that United States continues to seek a "complete denuclearisation of North Korea".
"We are talking about putting a live nuclear warhead on a missile that has been tested only a handful of times". Trump also mocked North Korean leader Kim Jong Un in the speech, dubbing him "Rocket Man".
North Korea conducted its sixth and most powerful nuclear bomb test on September 3, prompting another round of United Nations sanctions.
"If (North Korea) did, it would be condemned by everyone - the Chinese and the Russians would be just as upset as the U.S.", William McKinney, a scholar at the U.S. -Korea Institute of the Johns Hopkins School of Advanced International Studies, told Bloomberg. The North Korean also said that Trump comments were reflective of "mentally deranged behaviour".
"This is not a rhetorical expression loved by Trump", Kim was quoted as saying.
Trump has traded rhetorical barbs with North Korea as those tests were carried out.
At a Friday night rally for Republican U.S. Senate contender Luther Strange in Alabama, Mr. Trump derided "little rocket man" - his new favorite term for Kim - and emphasized that North Korea would be dealt with. He defended the country's nuclear program as a necessary deterrent against USA aggression.