National Security Adviser H.R. McMaster warned North Korean dictator Kim Jong Un should not be sleeping easily at night and said the evolving situation with the North Koreans constitutes a "grave threat" to the U.S.

McMaster made the remark in an interview Wednesday and emphasized that Kim has become increasingly isolated on the world stage.

"No, I think he should not be," McMaster said after MSNBC's Hugh Hewitt asked if Kim should be "sleeping easily at night."

"Because he has the whole world against him, right? He's isolated. He's isolated on this. Since 1953 the Korean peninsula has been in a state of armistice. The war never formally ended and there's been no aggression, no aggression from the United States, South Korea, any of our allies."

The national security adviser also said he isn't sure whether things would change in North Korea if the young dictator were taken out of power and argued his behavior means the future of the regime is "almost impossible to predict."

"Well, I'm not sure about that," McMaster said. "I don't think anyone has a very clear picture of the inner workings of that regime."

"What is clear is that it is an authoritarian dictatorship that has existed since the end of World War II. It is now in its third generation. And there is a difference in this third autocratic ruler in that he's as brutal as the previous two had been. But he's doing some things differently, he's killing members of his own family," he continued. "And so, what this means for the future of that regime I think is almost impossible to predict."

He also would not confirm a Reuters report that North Korea has tested intercontinental ballistic missiles that could reach anywhere in the U.S.

"I'm not going to confirm it," McMaster said. "But as I mentioned, really, whether it could reach San Francisco or Pittsburgh or Washington. How much does that matter, right? It's a grave threat."