Donald Trump has claimed talks with Kim Jong-un broke down because the North Korean leader wanted all sanctions lifted – something the US could not agree to.

Trying desperately to put a positive spin on a humiliating turn of events – one that appeared to shock observers and participants alike – the US president said he was not prepared to make a deal for the sake of it. “Sometimes you have to walk,” said the man who had bragged on the presidential campaign trail of his skills as a deal maker.

He said the sticking point had been the North Korean leader’s demand to have lifted all of the US and international sanctions imposed on it. “Basically they wanted the sanctions lifted in their entirety, and we couldn’t do that.”

He insisted that the two sides would talk again and that his relationship with the 35-year-old North Korean leader was “very warm”. He insisted that the meeting did not end contentiously but with “a very friendly walk”. “I’d much rather do it right than do it fast. We’re in position to do something very special.”

In recent days, Mr Trump had sounded cautious about the prospect of securing a rapid breakthrough with North Korea, with which the US had been at loggerheads for seven decades. After last June’s meeting in Singapore made history, he travelled to Vietnam insisting to reporters he was in no rush.

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All of this led experts to ask why he was apparently so keen for a second summit without the ground work to edge the two countries closer being completed by officials.

Summits that are scheduled to involve a ceremony to sign an agreement almost invariably follow months of negotiations and discussions.

“The two leaders discussed various ways to advance denuclearisation and economic driven concepts,” said White House press secretary Sarah Huckabee Sanders. “No agreement was reached at this time, but their respective teams look forward to meeting in the future.”

Yet as he prepared to fly back to Washington empty handed and three hours ahead of schedule - his former lawyer Michael Cohen and his allegations of presidential wrongdoing dominating the headlines – Mr Trump admitted there was no plan yet for a third summit.

The president said Mr Kim had been prepared to move some way towards denuclearisation.

President Trump and Kim Jong Un chat outside the Sofitel Metropole before extended meeting at summit in Hanoi

“He wants to denuke, he just wants to do areas that are less important than what we want,” he said. “He has a certain vision and it’s not exactly our vision, but it’s a lot closer than it was a year ago and I think eventually we’ll get there. For this particular visit we decided that we had to walk.”

He added: “We haven’t given up anything. They have tremendous potential, unbelievable.”

Secretary of state Mike Pompeo, part of Mr Trump’s negotiating team, said Mr Kim was “unprepared” to meet US demands. Earlier, the North Korean leader told reporters his country is willing to denuclearise – or else he “would not be here”.

“We didnt get to something that made sense for the United States of America. I think Chairman Kim was hopeful that we would. We asked him to do more. He was unprepared to do that. But I’m still optimistic,” said Mr Pompeo.

There was no immediate response from Mr Kim or North Korean leader. He is due to stay in Vietnam for another two days.

Analysts had pointed out Mr Kim would want major concessions before he was willing to give up his status as a nuclear weapons nation.

“It is little wonder these negotiations broke down after Trump has spent more time in office blowing up nuclear treaties than building them,” Akira Kawasaki of the International Committee to Abolish Nuclear Weapons’ International Steering Group, told CNN.

“We need a real plan rooted in the international community and treaties like the Treaty on the Prohibition of Nuclear Weapons, which the Koreas could join tomorrow and begin the disarmament process with legitimacy.”

Responding to a question about whether South Korean President Moon Jae-in had hit a “glass ceiling” when it came to pursuing peace on the Korean Peninsula, Mr Trump said he would speak to the South Korean leader on Thursday.