In a letter to Kim, Trump announced he would not go ahead with the high-stakes meeting set for June 12 in Singapore, and would instead pursue Washington's "maximum pressure campaign" through sanctions on Kim's regime.

Just before Trump announced the cancellation of the talks, North Korea declared it had "completely" dismantled its nuclear test site, in a carefully choreographed move portrayed by the isolated regime as a goodwill gesture ahead of the summit.

But the chances of success for the talks, which would have been an unprecedented face-to-face between a US and North Korean leader that Washington hoped would result in full denuclearization of the North, had recently been thrown into doubt on both sides.

Trump's announcement -- which prompted South Korea's president to convene crisis talks of his top security advisors -- came one day after Pyongyang hardened its rhetoric by attacking Vice President Mike Pence as "ignorant and stupid."

"Sadly, based on the tremendous anger and open hostility displayed in your most recent statement, I feel it is inappropriate, at this time, to have this long-planned meeting," read Trump's letter to Kim, released by the White House.

"The world, and North Korea in particular, has lost a great opportunity for lasting peace and great prosperity and wealth. This missed opportunity is a truly sad moment in history," he said.

The US leader brandished the threat of America's nuclear might in his letter, writing: "You talk about your nuclear capabilities, but ours are so massive and powerful that I pray to God they will never have to be used."

And in later comments from the White House, Trump warned that South Korea and Japan stood ready to respond, along with the United States, "should foolish or reckless acts be taken by North Korea."

"In the meantime, our very strong sanctions, by far the strongest sanctions ever imposed, and maximum pressure campaign will continue," Trump added.

The Republican president held out hope that a meeting with Kim was still possible, stressing he had been looking forward to the event -- talks which led him to openly entertain the notion it could earn him a Nobel Peace Prize.

"It's possible the existing summit could take place, or a summit at some later date. Nobody should be anxious. We have to get it right," Trump said.

"If and when Kim Jong Un chooses to engage in constructive dialogue and actions, I am waiting."

- 'Rocking and ready' -

Politically, Trump had invested heavily in the success of the planned summit. Privately, most US officials, as well as outside observers, believed it would go ahead despite the recent uptick in tensions.

Trump had touted the talks as a golden opportunity for Pyongyang -- telling Fox News in an interview recorded Wednesday there was "a good chance" they would go ahead as planned.

Hand-picked US aides travelled to Singapore this week where they were expected to meet their North Korean counterparts and iron out details of the meeting.

But as the date drew nearer, the gulf in expectations between the two sides had been made clear.

Washington has made it clear it wants to see the "complete, verifiable and irreversible denuclearization" of the North.

But Pyongyang has vowed it will never give up its nuclear deterrence until it feels safe from what it terms US aggression.

It did however apparently proceed with the dismantling of its Punggye-ri test site in the country's northeast.

A small group of journalists invited to the scene described a series of explosions throughout the day. Three of them were in entry tunnels to the underground facility, followed by blasts that demolished a nearby barracks and other structures.

The Punggye-ri test facility is buried inside a mountain in North Hamgyong province, near the border with China and is North Korea's only known nuclear test site. It has been the staging ground for all six of the North's nuclear tests.

- 'Rocking and ready' -

Speaking after Trump's letter was released, Secretary of State Mike Pompeo -- who twice travelled to Pyongyang to lay the groundwork for the summit -- said it was scrapped because a "successful outcome" did not seem possible.

"Over the past many days, we have received no response to our inquiries from them," Pompeo told US lawmakers.

He reiterated however that "there was a real understanding between us" after his latest meeting with Kim, and that the American team had been "rocking and ready and prepared for this meeting".

UN Secretary-General Antonio Guterres urged the parties to keep talking despite the summit cancellation, as did host Singapore.

In Seoul, South Korean President Moon Jae-in expressed his "deep regret" and summoned his top security aides to the presidential Blue House for emergency talks, his press secretary Yoon Young-chan said in a message to reporters, according to the country's Yonhap news agency.

Officials in Seoul "are trying to figure out what President Trump's intention is and the exact meaning of it," Yonhap reported, quoting another presidential spokesman.