Sen. John McCain said Tuesday that President Trump should not threaten North Korea with "fire and fury" unless he is prepared to carry out those threats.

"The great leaders I've seen don't threaten unless they're ready to act, and I'm not sure President Trump is ready to act," McCain told the Arizona radio station KTAR. "I take exception to the president's comments because you got to be sure you can do what you say you're going to do."

The Republican chairman of the Senate Armed Services Committee said the U.S. should be focused on working with China and building up its missile defenses in the wake of a report that an updated intelligence assessment found North Korea now has the capability to miniaturize a nuclear warhead.

The assessment, reported by the Washington Post, means Kim Jong Un's regime has apparently cleared a key hurdle to striking the continental United States with a nuclear-tipped intercontinental ballistic missile.

The rogue regime had recently completed two successful tests of ICBMs that the Pentagon and experts believe show the capability to reach major American cities.

"North Korea best not make any more threats to the United States," said Trump, who was on a working vacation at his Bedminster, N.J. golf club when the news broke. "They will be met with fire and fury like the world has never seen."

McCain, who was in Arizona receiving cancer treatment, said he did not believe the North was prepared to go to war and that Trump's statements might have been partly bluster.

"It's not terrible in what he said. It's the classic Trump in that he overstates things," said McCain, according to quotes reported by KTAR.

U.S. military planners are deeply hesitant to start another war on the Korean peninsula because the North has thousands of artillery pieces aimed a nearby Seoul, South Korea, a metropolis of over 20 million people, and has shorter range missiles that could strike Japan.