When New York Times op-ed columnist Nicholas Kristof traveled North Korea recently, the five-day trip turned out to be "very different" from his prior two visits.

"North Korea is always a bizarre place and there's always a certain amount of over-the-top rhetoric. But this time the country has really galvanized for war," Kristof said Thursday on "CBS This Morning." "There's constant talk about missile attacks on the U.S. There are billboards around the country showing missiles destroying the U.S. Capitol, destroying the U.S. flag. There is discussion about how a nuclear war with the U.S. is inevitable, and maybe most striking, about how North Korea will defeat the U.S. in this nuclear war. And it's not only survivable but actually winnable."

Nicholas Kristof CBS News

Two days after a North Korean official said "a nuclear war may break out any moment," the regime warned Thursday the U.S. could face an "unimaginable" strike at an unexpected time.

"Astonishingly, they are convinced that they would win and the U.S. would then retreat ignominiously from the Korean peninsula, from Japan, from Asia, and [North Korean leader] Kim Jong Un would unite the Korean peninsula," Kristof said.

He added North Koreans spread the narrative that they've "repeatedly defeated the U.S. in the Korean War, in series of incidents across the DMZ."

"There's always a danger, of course, that dictators kind of believe their own propaganda. And I'm nervous that that is what is happening right now," Kristof said.

The Pulitzer Prize-winning journalist said he believes President Trump's hardline rhetoric against the regime is "counterproductive."

"It was striking that the North Koreans are leveraging it for their own propaganda. So your average North Korean knows nothing about Otto Warmbier, for example," Kristof said, speaking of the American student detained in North Korea who died in June after returning to the U.S. in a coma. "That doesn't penetrate. They know all about President Trump's threat to totally destroy North Korea because it fits into their narrative."

South Korean President Moon Jae-in told "CBS This Morning" co-host Norah O'Donnell in June that he would like to have "dialogue" with Kim Jong Un, but Kristof said it appears the regime isn't interested.

"One of the sad things is that the doves, if you will, the people trying to find an exit ramp in North Korea, just like those in Washington, seem to be marginalized," Kristof said. "And so the hardliners seemed to be ascendant both in the North Korean capital, Pyongyang, and in Washington, so I was struck that the North Koreans were not very interested in talks."