New US Secretary of State Mike Pompeo said he had a "good conversation" with North Korea's Kim Jong Un during his visit to Pyongyang, adding Kim was "prepared to... lay out a map that would help us achieve" denuclearisation.

Pompeo made the remarks in an exclusive interview with ABC News, extracts of which were released ahead of its broadcast today.

Pompeo, who is currently in the Middle East on his first trip as Washington's chief diplomat, described Kim as "very well prepared" during their secret meeting, which took place over Easter weekend to set the groundwork for a historic summit meeting with US President Donald Trump.

"We had an extensive conversation on the hardest issues that face our two countries," he said.

"I had a clear mission statement from President Trump. When I left Kim Jong Un understood the mission exactly as I described it today." Trump, meanwhile, addressed the topic of the planned summit at a campaign-style rally in the town of Washington, Michigan.

"If we would have said where we are today from three or four months -- months ago, do you remember what they were saying? 'He's going to get us into nuclear war, they said,'" referring to a fiery war-of-words between himself and Kim that preceded a diplomatic breakthrough.

He added: "No, strength is going to keep us out of nuclear war, not going to get us in!" The US president added he was cautiously optimistic over the outcome.

"I think we will have a meeting over the next three or four weeks that will be a very important meeting... but we'll see how it goes.

"And again, whatever happens, happens. Look, I may go in. It may not work out. I leave," he continued, adding he would avoid the mistakes of the Obama administration which arrived at a denuclearization deal with Iran.

"We're going to have hopefully a very successful negotiation over the next three or four weeks. And we'll be doing the world a big favor. We'll be doing the world a big favor."