Strained relations soured further when US Secretary of State Mike Pompeo pulled out of talks with North Korean officials this week after Pyongyang complained Washington had not made any concessions in return for the moves it claims to have taken towards denuclearisation.

And insiders say the situation is very different to the one painted by Donald Trump.

The US President told a White House press briefing: “We’re very happy with how it’s going with North Korea.

“We think it’s going fine. We’re in no rush. We’re in no hurry. The sanctions are on. The missiles have stopped. The rockets have stopped. The hostages are home. The great heroes are home.”

Mr Trump said the talks were cancelled “because of trips that are being made” but did not elaborate.

US military officials, foreign diplomats and sources familiar with developments say the two sides are locked in a standoff over who will make concessions first.

And diplomats have reported Pyongyang officials are “really angry” about the US refusal to offer sanctions relief and claim personal friction between US and North Korean negotiators may be slowing progress.

Bruce Klingner, a senior fellow at the Heritage Foundation, said: “It doesn’t bode well for the negotiations, which were already not proceeding well.”

Mr Klingner, a former CIA deputy division chief for Korea, highlighted North Korea’s recent threat to restart “building up nuclear forces” if the US didn’t ease sanctions.

And he also pointed out North Koeran officials had yet to meet Mr Pompeo’s Special Representative for North Korea, Stephen Biegun, and that the two countries had still not agreed on the definition of basic terms such as “denuclearlisation” five months after Mr Trump’s historic summit with Kim Jong-un.

He said: “Clearly the two sides remain very far apart.”

Mr Trump said he still expected to hold a second summit with Kim early next year but insisted sanctions would not be lifted until North Korea gives up its weapons.

He said: “The sanctions are on. I’d love to take the sanctions off, but they have to be responsive, too.”

South Korea, which has worked to encourage US-North Korea dialogue, is trying to play down the growing tensions.

Foreign minister Kang Kyung-wha said North Korea had suggested a postponement.

She said: “The North side said ‘both of our schedules are busy, so let’s postpone’.”

Presidential spokesman Kim Eui-kyeom said Seoul did not believe it would mean the second summit could not take place and warned against “overthinking the postponement”.

Another officials said: ”I think we have to look at it as a part of the process of reaching complete denuclearisation and setting up a peace regime.”