The warning comes after the US president revived his “rocket man” nickname for Kim Jong Un and spoke of possible military action.
North Korea has threatened to renew its insults of Donald Trump and consider him a “dotard” if he keeps using provocative language against Kim Jong Un.
The country’s foreign ministry issued the warning days after the US president spoke of possible military action and revived his “rocket man” nickname for the North Korean ruler.
Choe Son Hui, Pyongyang’s first vice foreign minister, said Mr Trump’s remarks “prompted the waves of hatred of our people against the US” because they showed “no courtesy when referring to the supreme leadership of dignity” of North Korea.
She said North Korea will respond with its own harsh language if Mr Trump again uses similar phrases and shows that he is intentionally provoking North Korea.
“If any language and expressions stoking the atmosphere of confrontation are used once again… that must really be diagnosed as the relapse of the dotage of a dotard,” Ms Choe said.
North Korea first called Mr Trump a “dotard” in 2017, with the Oxford English Dictionary defining the term as “a person whose mental faculties are impaired, specifically, a person whose intellect or understanding is impaired in old age”.
During his visit to London this week, Mr Trump said his relationship with Mr Kim was “really good” but called for him to follow up on a commitment to denuclearise.
The US president said: “We have the most powerful military we ever had, and we are by far the most powerful country in the world and hopefully we don’t have to use it. But if we do, we will use it.”
Mr Trump added that Mr Kim “likes sending rockets up, doesn’t he? That’s why I call him rocket man”.
The president’s comments prompted North Korea’s military chief to warn that the use of force against the country would cause a “horrible” consequence for the US.
Pak Jong Chon said North Korea would take unspecified “prompt corresponding actions at any level” if the US takes any military action.
Mr Trump has previously said he would rain “fire and fury” on North Korea and derided Mr Kim as “little rocket man”, while the North Korean leader questioned the US president’s sanity and said he would “tame the mentally deranged US dotard with fire”.
However, the two leaders have avoided such words and developed better relations after North Korea entered nuclear negotiations with the US last year, with Mr Trump even saying he and Mr Kim “fell in love”.
The pair held face-to-face talks aimed at denuclearisation in Singapore in June 2018 and staged a failed summit in Vietnam in February this year.
But talks have stalled since then, and despite another meeting in the demilitarised zone that separates North and South Korea in June, Pyongyang has restarted testing of short-range ballistic missiles.
Mr Trump’s national security adviser, Robert O’Brien, said the US remains hopeful that a deal can be reached with North Korea.
He said: “I don’t want to say we’re optimistic, but we have some hope that the Koreans will come to the table… and we can get a deal.”
