North Korean Supreme Leader Kim Jong-un is never going to give up, and it is time the United States starts thinking about regime change, whether the U.S. drives for it itself or presses on China that it takes action against the country, former Green Beret commander Michael Waltz said Wednesday.

"I worry about that the Chinese, after the meeting with President [Donald] Trump at Mar-a-Lago basically said, we'll take care of this North Korea problem," Waltz, a Fox News contributor, told the "America's Newsroom" program.

Waltz said, though, he does believe the United States is heading toward a military solution.

"Everybody is focused on the ICBM," he said. " I'm worried that a nuclear warhead could be put on a shorter range missile that could hit Tokyo or other allies in the region. That could happen even more quickly. So, look. Again, I don't think Kim Jong-un is going to give up on this program. We can go back to talks and go back to more sanctions. But that needs to happen very quickly."

The United States, he continued, can't be faced with the prospect of seeing a missile being fueled up before taking action.

"The other point is our long-range missile intercept only had about a 50 percent success rate," said Waltz. "I'm not willing to give a 50 percent chance of a missile hitting Tokyo, Seoul or Alaska."

However, China has not stepped up, Waltz said, even though there were some initial good signs, and trade has even increased between China and North Korea.

"They haven't really done what they need to do to clamp down on North Korea's missile program," Waltz said. "The Chinese calculus needs to change."

China is worried North Korea will either collapse or that if he is out office, the Korean Peninsula will unite and will be friendly to the United States, said Waltz.

"Then they [would be] faced with U.S. troops on their border," said Waltz. "That needs to change, to where the Chinese are more worried about war on the Korean peninsula and a pre-emptive U.S. strike to take the program out."

There is much more the Chinese can do to put an economic squeeze on Kim's regime, said Waltz, and actions the United States could take as well, but using military action would be difficult.

"We need to understand that the North Koreans have been digging in, preparing for this for over 50 years," said Waltz. "These things are built into bunkers and caves, into the sides of mountains. They are prepared to hit Seoul, South Korea very hard with artillery and missiles should war break out. There's no good military option here."

And if Seoul is hit, that would be devastating, he said, comparing a strike to "artillery raining into [a place] the size of Manhattan."