US President Donald Trump in February cut short a summit in Hanoi with North Korean leader Kim Jong Un, with Pyongyang later blaming Pompeo for a pushing a hard line and calling for his exclusion from future negotiations.

In an interview with CBS News, Pompeo said the Hanoi summit had more "nuance" than publicly reported, with the two sides sharing their positions.

"It's going to be bumpy. It's going to be challenging. I hope we get several more chances to have serious conversations about how we move this process forward," Pompeo said.

North Korea has demanded an easing of sanctions and Trump has indicated sympathy, saying he is fond of Kim.

But Pompeo has insisted on maintaining pressure until a comprehensive deal on ending North Korea's nuclear program.

Pompeo said that years of previous diplomatic efforts had made a mistake with North Korea by handing them "a bunch of money in exchange for too little."

"We're determined not to make that mistake, and I think the North Koreans now see that pretty clearly," he said.

Pompeo, who traveled to Pyongyang four times last year, said he "absolutely" believed that Kim was willing to take a major step to give up his nuclear weapons in return for less isolation.

"Only time will tell for sure, but I've seen enough to believe that there is a real opportunity to fundamentally shift the strategic paradigm on the peninsula there."

His remarks came as Kim flew to Russia's far east for a summit with President Vladimir Putin, whose country has historically been an ally of North Korea.