US Secretary of State Mike Pompeo has brushed off North Korean charges he used "gangster-like" diplomacy in negotiations in Pyongyang, suggesting Kim Jong-un follows Vietnam's path in overcoming past hostilities with the United States.

Key points: Mr Pompeo said his meeting with North Korean officials included planning steps for denuclearisation

Mr Pompeo said his meeting with North Korean officials included planning steps for denuclearisation He appealed to Mr Kim to follow the steps of Vietnam's 'miracle' relationship with the US

He appealed to Mr Kim to follow the steps of Vietnam's 'miracle' relationship with the US He said US-Vietnam trade has grown 8,000 per cent since the normalisation of relations in 1995

Mr Pompeo said there was still a lot of work to do, but he was confident the North Korean leader would stick to a commitment to abandon nuclear weapons he made during a summit with US President Donald Trump in Singapore last month.

Mr Pompeo's meeting with Japan's Minister of Foreign Affairs, Taro Kono, and South Korean Foreign Minister, Kang Kyung-wha, followed Mr Pompeo's two days of talks in Pyongyang that ended on Saturday.

"When we spoke to them about denuclearisation, they did not push back," Mr Pompeo told a news conference.

"If those requests were gangster-like, the world is a gangster, because there was a unanimous decision at the UN Security Council about what needs to be achieved.

"The road ahead will be difficult and challenging and we know that critics will try to minimise the work that we've achieved."

He added that his two days of talks with senior North Korean officials had "made progress" and included a "detailed and substantive discussion about the next steps towards a fully verified and complete denuclearisation".

Mr Pompeo spent the night at government guesthouse Park Hwa in Pyongyang. ( AP: Andrew Harnik )

Mr Pompeo said the talks "brought us in a dangerous situation where we may be shaken in our unshakable will for denuclearisation, rather than consolidating trust".

The statement was carried by the official KCNA news agency on Saturday soon after Mr Pompeo left Pyongyang, raising questions about the future of the talks in which he is trying to persuade Pyongyang to give up a nuclear weapons programme that threatens the United States.

Those include the formation of a working group to determine exactly how North Korea's denuclearisation will be verified and a Thursday meeting with Pentagon officials to discuss the return of remains of American soldiers killed during the Korean War.

Mr Pompeo also sought to dispel suggestions the Trump administration had backed down from demanding the complete, verifiable and irreversible dismantlement of the North's nuclear weapons.

He said North Korea understood that denuclearisation must be "fully verified" and "final".

South Korean Foreign Minister Kang Kyung-wha said North Korea had balked at a written pledge for "complete, verifiable and irreversible denuclearisation" for historical reasons but stressed that the goal remained the same whether that exact phrase was used.

Fully verified, final denuclearisation "isn't any softer in stating our shared goal of complete denuclearisation," she said.

Despite what he described as progress, Mr Pompeo said the results so far did not warrant any easing of sanctions, which he said would be enforced "with vigour" until North Korea follows through with denuclearisation.

The Vietnam 'miracle can be yours'

Mr Pompeo met with top Vietnamese officials including Communist Party General Secretary Nguyen Phu Trong. ( AP: Andrew Harnik )

Speaking later to members of the US-Vietnamese business community in Hanoi, Mr Pompeo called on Mr Kim to replicate Vietnam's "miracle" of economic growth by improving ties with the US, vowing that America keeps its promises with former foes.

Mr Pompeo said Vietnam's experience since the normalisation of relations with the US in 1995 should be proof for North Korea that prosperity and partnership with the US is possible after decades of conflict and mistrust.

"We know it is a real possibility because we see how Vietnam has travelled this remarkable path," Mr Pompeo said.

"In light of the once-unimaginable prosperity and partnership we have with Vietnam today, I have a message for Chairman Kim Jong Un: President Trump believes your country can replicate this path," he said, repeating Mr Trump's pledge to help improve North Korea's economy and provide it with security assurances in return for Mr Kim giving up nuclear weapons.

"It's yours if you'll you seize the moment. This miracle can be yours. It can be your miracle in North Korea as well," Mr Pompeo said.

Mr Pompeo said that in past two decades, US bilateral trade with Vietnam had grown 8,000 per cent, and American companies had poured in billions of dollars of investments.

"If they are able to do this, they will be remembered, and Chairman Kim will be remembered, as a hero of the Korean people," Mr Pompeo said.

AP/Reuters