President Moon Jae-in bid farewell to Kim Jong-un with a triple hug after their summit at the truce village of Panmunjom on Saturday - REUTERS

American officials crossed into North Korea on Sunday to press ahead with preparations for an on-off summit between Donald Trump and Kim Jong-un, the latest twist in a frantic round of diplomatic manoeuvring to salvage the meeting.

Hours earlier Mr Trump said he believed the summit could still place on June 12 as planned despite his abrupt decision to cancel.

Meanwhile, the South Korean president met Kim and declared the North Korean leader to be committed to the “complete denuclearisation of the Korean peninsula”.

It leaves analysts warning that the result could be little more than a hurriedly arranged photo opportunity between Mr Trump and Kim, rather than an historic opportunity to usher in a new era of peace and stability.

Even so, planning continues.

Korean detente How did we get here?

American and South Korean media reported that Sung Kim, a former US ambassador to South Korea who has taken part in past nuclear negotiations with Pyongyang, had arrived for talks with Choe Son Hui, the North Korean vice foreign minister.

The Washington Post, citing an official familiar with the plans, said he was accompanied by Allison Hooker, the Korea specialist on the National Security Council.

It said the meetings were expected to continue until Tuesday at Tongilgak, or “Unification House”, the building in the DMZ where Kim met Moon Jae-in, the South Korean president, on Saturday night for impromptu talks to save the summit .

Mr Moon told reporters that he and Mr Kim agreed the summit should take place and said the North Korean leader “again made clear his commitment” to denuclearisation.

But he added that Pyongyang had doubts that Washington would guarantee its stability and security.

“What Kim is unclear about is that he has concerns about whether his country can surely trust the United States over its promise to end hostile relations and provide a security guarantee if they do denuclearisation,” Mr Moon said.

South Korea's President Moon Jae-in walks with North Korea's leader Kim Jong-un for their second summit Credit: AFP

He has emerged as an optimistic go-between, repeatedly talking up Mr Kim’s commitment to progress despite doubts elsewhere that the North Korean regime would ever give up weapons it has long insisted were key to its survival.

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Victor Cha, the former director of Asian affairs on the National Security Council and who was expected to become Mr Trump’s ambassador to Seoul until he publicly broke with White House policy, said the focus on summit logistics overshadowed the real stumbling block.

“We’re all focussed on the rollercoaster but in terms of the substance the key issue is: Are they going to give up their nuclear weapons? And I think unfortunately the answer is no,” he told NBC’s Meet the Press.

Mr Trump stunned the world earlier this year when he set aside months of angry rhetoric to accept North Korea’s invitation to face-to-face talks.

Donald Trump N Korea letter

Hopes of a breakthrough seemingly evaporated on Thursday, however, when Mr Trump abruptly cancelled the plans citing North Korean “hostility”.

But within a day he was expressing second thoughts and at the White House late on Saturday he said preparations were still under way.

“It's moving along very nicely,” he said. “We're looking at June 12 in Singapore. That hasn't changed.”

He also confirmed that talks were continuing.

“As you know there are meetings going on as we speak in a certain location which I won’t name, but you'd like the location,” he said.