Trump has touted the North's suspension of nuclear and ICBM tests as one of his key achievements.

Trump warned in response that the US may use military force against North Korea if necessary and referred to North Korean leader Kim Jong-un as "Rocket Man." The North said Trump's remarks, if deliberate, should be "diagnosed the relapse of the dotage of a dotard."

Earlier Saturday, North Korea's ambassador to the United Nations, Kim Song, said that denuclearization has already been taken off the negotiating table with the US.

"We do not need to have lengthy talks with the US now and denuclearization is already gone out of the negotiating table," Kim said in a statement issued after Britain and five other European nations condemned the North's "continued testing of ballistic missiles."

Trump, meanwhile, insisted he has "a very good relationship" with Kim Jong-un and added, "I think we both want to keep it that way."

"I think he'd like to see something happen," Trump said. "But there is a certain hostility. There's no question about it."

As for the state of inter-Korean ties, Trump said, "I don't know that (Kim's) relationship with South Korea is very good. But we're going to find out."

There has been scant progress in denuclearization talks between the US and North Korea, following the collapse of the second Trump-Kim summit in February.

Pyongyang has set a year-end deadline for Washington to offer concessions in nuclear talks. It has threatened to terminate the dialogue phase and adopt a "new way" if the US refuses to change tack. (Yonhap)