US President Donald Trump has abruptly cancelled his top diplomat's planned trip to North Korea, publicly acknowledging for the first time that his effort to get Pyongyang to denuclearise had stalled since his summit with the North's leader.

Mr Trump partly blamed China for the lack of progress with North Korea and suggested that talks with Pyongyang, led so far by Secretary of State Mike Pompeo, could be on hold until after Washington resolved its bitter trade dispute with Beijing.

It was a dramatic shift of tone for Mr Trump, who had previously hailed his 12 June summit with North Korean leader Kim Jong Un as a success and said the North Korean nuclear threat was over, despite no real sign Pyongyang was willing to give up its nuclear weapons.

But Mr Trump still kept the door open to a second summit with Mr Kim, with whom the president recently said he has "great chemistry."

"I have asked Secretary of State Mike Pompeo not to go to North Korea, at this time, because I feel we are not making sufficient progress with respect to the denuclearisation of the Korean Peninsula," he wrote on Twitter.

The North Korean mission to the United Nations declined to comment.

Negotiations have been all but deadlocked since the June summit in Singapore.

Mr Pompeo has pressed for tangible steps toward North Korea's abandonment of its nuclear arsenal while Pyongyang is demanding that Washington first make concessions of its own.

Mr Trump's statement came just a day after Mr Pompeo said he would again visit North Korea and would take his new special envoy, former auto industry executive Stephen Biegun, with him.

But President Trump asked Mr Pompeo not to go during a meeting yesterday, and they crafted the tweets together, White House officials said.

National security adviser John Bolton, considered a leading North Korea hawk, weighed in by speakerphone during a visit to Ukraine, US officials said, speaking on condition of anonymity.

Many other key officials learned of Mr Trump's decision by seeing the crawl across a television screen, some during a meeting on North Korea negotiations, officials said.

Some US intelligence and defense officials had considered Mr Pompeo's latest trip to be premature and said the prospects for significant progress appeared dim.

Mr Pompeo, who would have been making his second visit to Pyongyang since the summit, had not been due to meet Mr Kim this time.

Mr Trump himself was still open to another meeting with Kim, in hopes of advancing the process, but was not pleased with the latest signals from North Korea, a White House official said.

South Korean Foreign Minister Kang Kyung-wha has spoken to Mr Pompeo on the phone and expressed concern over the delay of his visit.

Ms Kang asked Mr Pompeo to keep the momentum of dialogue with North Korea to establish denuclearisation and peace on the Korean peninsula, according to the Foreign Ministry's news release.

Trump put some of the onus on China, North Korea's biggest trading partner and a crucial actor in enforcing sanctions to keep pressure on Pyongyang.

"Because of our much tougher Trading stance with China, I do not believe they are helping with the process of denuclearization as they once were (despite the UN Sanctions which are in place)," Mr Trump said on Twitter.

"Secretary Pompeo looks forward to going to North Korea in the near future, most likely after our Trading relationship with China is resolved," Mr Trump wrote.

"In the meantime I would like to send my warmest regards and respect to Chairman Kim. I look forward to seeing him soon!"

President Trump told Reuters on Monday he believed Mr Kim had taken specific steps toward denuclearisation and that they would "most likely" meet again.