North Korea has insulted US President Donald Trump, calling him a “heedless and erratic old man”.

The insult comes after Mr Trump tweeted that North Korean leader Kim Jong Un would not want to abandon a special relationship between the two leaders and affect the American presidential election by resuming hostile acts.

A senior North Korean official, former nuclear negotiator Kim Yong Chol, said that his country would not cave in to US pressure because it has nothing to lose and accused the Trump administration of attempting to buy time ahead of an end-of-year deadline set by Kim Jong Un for Washington to salvage nuclear talks.

On Sunday, Mr Trump tweeted: “Kim Jong Un is too smart and has far too much to lose, everything actually, if he acts in a hostile way … North Korea, under the leadership of Kim Jong Un, has tremendous economic potential, but it must denuclearise as promised.”

He was referring to a vague statement issued by the two leaders during their first summit in Singapore in June last year that called for a nuclear-free Korean Peninsula without describing when or how it would occur.

Mr Trump added that Mr Kim “does not want to void his special relationship with the President of the United States or interfere with the U.S. Presidential Election in November.”

Kim Yong Chol said Mr Trump’s tweets clearly show that he is an irritated old man “bereft of patience”.

“As (Trump) is such a heedless and erratic old man, the time when we cannot but call him a ‘dotard’ again may come,” Kim Yong Chol said.

“Trump has too many things that he does not know about (North Korea). We have nothing more to lose. Though the US may take away anything more from us, it can never remove the strong sense of self-respect, might and resentment against the U.S. from us.”

Kim Yong Chol travelled to Washington and met with the US president twice last year while setting up the summits with Kim Jong Un.

The latest war of words came as diplomats said the US had changed its mind and is now refusing to sign a letter that would have authorised the UN Security Council to hold a meeting on the human rights situation in North Korea.

Without support from Washington, the diplomats said European and other supporters of holding a meeting cannot go ahead because they are one vote short of the minimum nine “yes” votes required.

Nuclear negotiations faltered after a February meeting between Mr Trump and Mr Kim in Vietnam broke down when the US side rejected North Korean demands for broad sanctions relief in exchange for a partial surrender of its nuclear capabilities.

Mr Kim has said North Korea will seek a “new way” if the US maintains its sanctions and pressure, and issued the deadline for the Trump administration to offer mutually acceptable terms for a deal.

Mr Trump and Mr Kim met for a third time in June at the border between the two Koreas and agreed to resume talks. But an October working-level meeting in Sweden broke down over what the North Koreans described as the Americans’ “old stance and attitude”.