Trump's tweet last week, in which he boasted about having a "nuclear button" that is "much bigger and more powerful" than Kim's, helped send that message, according to Pompeo.

He rejected accusations that the president spoke lightly of the possibility of nuclear war.

"We in this administration understand the seriousness of what it is we are undertaking. We understand the threat," Pompeo said.

The American spy chief also questioned North Korea's sincerity in coming out for high-level talks with South Korea Tuesday. Although the meeting is expected to focus on the North's possible participation in next month's Winter Olympics in PyeongChang, South Korea, it could also help lower tensions over Pyongyang's nuclear and ballistic missile programs.

"The North Koreans are behaving out of fear. That is, they are very concerned that America, for the first time in an awfully long time, is serious about denuclearizing the peninsula," Pompeo said. "And I think they are trying to find a foothold, trying to find a place to reach out. And we'll just have to wait and see how the conversations go Tuesday." (Yonhap)