BRIDGEWATER, N.J. — President Donald Trump threatened North Korea “with fire and fury like the world has never seen” on Tuesday after suggestions the communist country has mastered one of the final hurdles to being able to strike the United States with a nuclear missile.

North Korea fired off its own “serious warning to the United States” about “enveloping” America’s Pacific territory of Guam in missile fire to counteract U.S. bombers that are based there.

The competing threats escalated tensions between the foes even further. Although it wasn’t clear if Trump and the Koreans were responding directly to each other, the heightened rhetoric added to the potential for a miscalculation that might bring the nuclear-armed nations into conflict.

Trump’s stern words to the camera at his golf course in Bedminster, N.J., came hours after reports indicating North Korea can now wed nuclear warheads with its missiles, including those that may be able to hit the American mainland. The isolated and impoverished dictatorship has strived for decades to have the ability to strike the U.S. and its Asian allies, and the pace of its breakthroughs is already having far-reaching consequences for stability in the Pacific and beyond.

The nuclear advances were detailed in an official Japanese assessment and a Washington Post story that cited U.S. intelligence officials and a confidential Defense Intelligence Agency report. The U.S. puts the North Korean arsenal at up to 60 nuclear weapons, more than double most assessments by independent experts, according to the Post.

“North Korea had best not make any more threats to the United States,” said a stern-looking Trump. “They will be met with fire and fury like the world has never seen. He has been very threatening beyond a normal state. And as I said they will be met with fire, fury and frankly power the likes of which this world has never seen before.”

Pyongyang had threatened the U.S. in response to the U.N. Security Council’s adoption this weekend of new, tougher sanctions spearheaded by Washington.