Pompeo and North Korean Foreign Minister Ri Yong Ho had been expected to meet on the sidelines of a South-east Asia security forum in Bangkok this week, but Ri cancelled his trip to the conference, a diplomatic source said.

On Tuesday, the senior US official also said it appeared Ri would not be in Bangkok.

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The most recent contact between North Korea and the United States occurred last week, when a US official, in Asia for unrelated talks, travelled to the demilitarised zone between the two Koreas to deliver photographs commemorating the June 30 meeting there between US President Donald Trump and North Korean leader Kim Jong Un, the senior US administration official told reporters.

Pompeo said on Monday he hoped working-level talks to revive denuclearisation talks with North Korea could occur "very soon," but emphasised that a follow-up leaders' summit was not planned.

Pompeo left Washington on Tuesday for Thailand and will also visit Australia and Micronesia in a trip lasting until Aug 6.

A February summit in Vietnam between Trump and Kim collapsed after the two sides failed to reconcile differences between Washington's demands for Pyongyang's complete denuclearisation and North Korean demands for sanctions relief.

At their DMZ meeting they agreed to resume working-level talks, but Pyongyang has since accused Washington of breaking a promise by planning to hold joint military exercises with South Korea in August and warned that these could derail the dialogue.

Trump told reporters at the White House on Tuesday: "We'll see what happens. I can't tell you what's going to happen."

North Korea has also warned of a possible end to its freeze on nuclear and long-range missile tests in place since 2017, which Trump has repeatedly upheld as evidence of the success of his engagement with Kim.