Donald Trump has warned about a "major, major conflict" between the US and North Korea, saying a catastrophic confrontation with the isolated state was "absolutely" possible.
In an interview ahead of his 100th day in office, the President said he was committed to resolving the diplomatic crisis peacefully.
But he added: “There is a chance that we could end up having a major, major conflict with North Korea. Absolutely.”
Speaking to the Reuters news agency, Mr Trump said the actions by Pyongyang were his biggest global worry.
He also lavished praise on Chinese President Xi Jinping for Chinese assistance in trying to rein in North Korea, saying he was a “very good man” who he had got to know “very well”.
"I believe he is trying very hard. He certainly doesn’t want to see turmoil and death. He doesn’t want to see it,” Mr Trump said.
Asked if he considered North Korean leader Kim Jong-un to be rational, the Republican billionaire said: "He's 27 years old. His father dies, took over a regime. So say what you want but that is not easy, especially at that age.
"I'm not giving him credit or not giving him credit, I'm just saying that's a very hard thing to do. As to whether or not he's rational, I have no opinion on it. I hope he's rational.”
On Wednesday, the Trump administration declared North Korea "an urgent national security threat and top foreign policy priority".
It said it was focusing on sanctions and diplomatic pressure but that military strikes remained an option.
However, any direct US military action would run the risk of massive North Korean retaliation and huge casualties in Japan and South Korea – and US forces in both countries.
Additional reporting Reuters