BEDMINSTER, N.J. – President Donald Trump escalated his rhetoric about North Korea's nuclear weapons program, threatening here Thursday that "things will happen to them like they never thought possible" should the isolated country attack the United States or its allies.

Trump told reporters that his Tuesday statement warning of "fire and fury" may not have been "tough enough," but even as he stepped up his brinksmanship with North Korean leader Kim Jong Un, the president sought to reassure anxious people around the world that he has the situation under control.

Trump would not say whether he is considering a preemptive strike on North Korea, and while he said he was open to negotiating with Pyongyang, he said talks over the years had done little to halt the country's nuclear program.

"What they've been doing, what they've been getting away with, is a tragedy, and it can't be allowed," Trump said.

Trump's comments come as his administration has struggled to project a unified front amid an ongoing internal debate over a strategy to confront North Korea.

The crisis is unfolding as the president is secluded at his private golf club in Bedminster, New Jersey, where he is spending most of his 17-day working vacation. On Wednesday, Vice President Mike Pence jetted to New Jersey to have lunch with Trump and attend a security briefing along with White House Chief of Staff John Kelly and national security adviser H.R. McMaster.

On Tuesday, Trump delivered an unusually bellicose threat to North Korea, warning that further provocations from Pyongyang "will be met with fire and fury like the world has never seen."

Trump improvized his statement, the language of which was not reviewed by his national security advisers or political aides.

In the 24 hours that followed, senior administration officials sought to calm jittery world leaders as well as Americans. But the statements from Secretary of State Rex Tillerson, Secretary of Defense James Mattis and senior White House officials, including adviser Sebastian Gorka, varied in substance and especially in tone. They ranged from sober and reassuring (Tillerson) to forceful yet measured (Mattis) to bellicose in the style of the president (Gorka).

The North Koreans effectively laughed off Trump's "fire and fury" threat, calling his statement "a load of nonsense." And they also threatened to fire missiles over the waters off Guam, a strategically-located Pacific island and home to a U.S. military base.

Asked Thursday morning whether Trump's thinking on the North Korean nuclear crisis had evolved in the wake of the threat to Guam, Sarah Huckabee Sanders, the White House press secretary, said it had not.

"Certainly nothing has changed in the president's thinking," Sanders told reporters. "He's made clear how he feels on that front."