Both sides have bristled at the insults; North Korea's first vice foreign minister expressed "displeasure" at Trump's comments, while Biegun condemned North Korea's statements about the US and its allies as "hostile," "negative," and "so unnecessary."

He also seemed to address North Korea's recent tests on Monday, warning that any North Korean provocation in the coming days would be "most unhelpful in achieving lasting peace on the Korean Peninsula."

"But it does not have to be this way," he said. "It is not yet too late."

Diplomats from Pyongyang and Washington have been attempting to negotiate a deal that would see Kim give up the country's nuclear weapons and the ballistic missiles used to deliver them in exchange for relief from punishing US and UN sanctions that have crippled the North Korean economy.

There appeared to be slow, small signs of progress, as Trump and Kim touted their friendly relationship and met three times in the hopes of striking a deal. But since the talks have stalled, North Korea has continually blamed the US for the lack of progress in nuclear negotiations.

Speaking in London on the sidelines of a NATO summit earlier this month, Trump said "we'll see what happens" when it comes to North Korea.