US Secretary of State Mike Pompeo was in Iowa Monday to discuss trade with farmers but also to engage teenagers on his job as America's top diplomat, including his work on last week's summit between President Donald Trump and North Korean leader Kim Jong-un.

Speaking at Johnston High School in Johnston, Iowa, Pompeo asked the students whether they had watched Trump on TV during his meeting with Kim in Hanoi, Vietnam.

Trump, the top US diplomat said, was "working to try and get the nuclear weapons out of North Korea."

"We made some progress," he said. "We didn't get to where we had hoped to be, and I think there's a lesson in that. I think there's a lot more work to do there."

Trump and Kim cut their second summit short without reaching an agreement on dismantling the North's nuclear weapons program.

Trump said he couldn't accept the North Koreans' demand for complete removal of sanctions, although the North later retorted that it had only asked for partial sanctions relief.

Pompeo said he hasn't given up on getting North Korea to denuclearize.

"The threat that's posed to the United States, to the next generation of Americans from North Korea's nuclear weapons, is a serious threat," he said.

"And my ambition as America's top diplomat is to try and convince them that they don't need their nuclear weapons, that they ought to change strategic course, they ought to begin to give up those weapons systems in a way that will allow the North Korean people to flourish and would reduce the risk here in America," Pompeo said. (Yonhap)