President Donald Trump said on Thursday a major conflict with North Korea is possible in the standoff over its nuclear and missile programs, but he would prefer a diplomatic outcome to the dispute.

"There is a chance that we could end up having a major, major conflict with North Korea. Absolutely," Trump told Reuters in an Oval Office interview ahead of his 100th day in office on Saturday.

Nonetheless, Trump said he wanted to peacefully resolve a crisis that has bedeviled multiple U.S. presidents, a path that he and his administration are emphasizing by preparing a variety of new economic sanctions while not taking the military option off the table.

"We'd love to solve things diplomatically but it's very difficult," he said.

Trump lavished praise on Chinese President Xi Jinping for Chinese assistance in trying to rein in North Korea. The two leaders met in Florida earlier this month.

"I believe he is trying very hard. He certainly doesn’t want to see turmoil and death. He doesn’t want to see it. He is a good man. He is a very good man and I got to know him very well.

"With that being said, he loves China and he loves the people of China. I know he would like to be able to do something, perhaps it's possible that he can’t," Trump said.

Trump spoke just a day after he and his top national security advisers briefed U.S. lawmakers on the North Korean threat and one day before Secretary of State Rex Tillerson will press the United Nations Security Council on sanctions to further isolate Pyongyang over its nuclear and missile programs.

The Trump administration on Wednesday declared North Korea "an urgent national security threat and top foreign policy priority." It said it was focusing on economic and diplomatic pressure, including Chinese cooperation in containing its defiant neighbor and ally, and remained open to negotiations.

U.S. officials said military strikes remained an option but played down the prospect, though the administration has sent an aircraft carrier and a nuclear-powered submarine to the region in a show of force.

Any direct U.S. military action would run the risk of massive North Korean retaliation and huge casualties in Japan and South Korea and among U.S. forces in both countries.

Trump, asked if he considered North Korean leader Kim Jong Un to be rational, said he was operating from the assumption that he is rational. He noted that Kim had taken over his country at an early age.

"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," he said.

Trump, sipping a Coke delivered by an aide after the president ordered it by pressing a button on his desk, appeared to rebuff an overture from Taiwan President Tsai Ing-wen, who told Reuters a direct phone call with Trump could take place again after their first conversation in early December angered Beijing.

China considers neighboring Taiwan to be a renegade province.

"My problem is that I have established a very good personal relationship with President Xi," said Trump. "I really feel that he is doing everything in his power to help us with a big situation. So I wouldn’t want to be causing difficulty right now for him."

"So I would certainly want to speak to him first."