WASHINGTON — President Donald Trump ramped up the rhetoric Wednesday against an increasingly hostile North Korea, warning the rogue regime that it is outmatched by what he touted as a U.S. nuclear arsenal “now far stronger and more powerful than ever before.”

Secretary of Defense Jim Mattis said Pyongyang should not initiate any action, because it “would lead to the end of its regime and the destruction of its people.”

Secretary of State Rex Tillerson took a more tempered tone and reassured Americans that they “should sleep well at night.”

Tillerson spoke with reporters en route to Guam, which North Korean state media said could be a target of its missiles. He said he saw no “imminent threat” to the region.

Trump a day earlier had promised to unleash “fire and fury” on North Korea should it continue its threats, though lawmakers, including Sen. John McCain (R-Ariz.), warned him against provocation.

North Korean dictator Kim Jong Un and his government had successfully miniaturized a nuclear warhead to fit on a missile, according to several news reports that cited U.S. intelligence. Kim has brazenly been conducting ballistic missile testing.

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Trump indicated Wednesday that the United States had updated its nuclear weapons cache since he took office, although he and White House aides could present no substantiation.

“My first order as President was to renovate and modernize our nuclear arsenal. It is now far stronger and more powerful than ever before,” he tweeted. “Hopefully we will never have to use this power, but there will never be a time that we are not the most powerful nation in the world!”

White House spokeswoman Lindsay Walters clarified that Trump was referencing a Jan. 27 presidential memorandum — among his first — to review the U.S. nuclear weapons cache.

She had no details about the president’s declaration of “stronger and more powerful” capabilities.

The North Korean military responded in a statement to Trump’s warning, calling it a “load of nonsense,” according to The Associated Press. The statement said that “only absolute force” can work on someone as “bereft of reason” as Trump.

It said North Korea will complete a plan by mid-August for the “historic enveloping fire at Guam,” convey it to the commander-in-chief of its nuclear force, and then “wait for his order,” the AP said. North Korea said it will “keep closely watching the speech and behavior of the U.S.”

Trump is in the midst of a working vacation at his Bedminster, New Jersey, golf club, where National Security Adviser H.R. McMaster is set to meet with him later this week.

Mattis explained Trump’s tweet as asserting military preparedness. “On taking office his first orders to me emphasized the readiness of our ballistic missile defense and nuclear deterrent forces,” the general said.

Tillerson defended the president’s language on another front, saying the “fire and fury” warning sent a strong message to Kim, who “doesn’t seem to understand diplomatic language.”

House Minority Leader Nancy Pelosi (D-Calif.) denounced the president’s words as reckless.

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“His saber-rattling and provocative, impulsive rhetoric erode our credibility and weaken our ability to reach a peaceful resolution to this crisis, and must immediately end,” she said.

Press Secretary Sarah Huckabee Sanders acknowledged that Trump on Tuesday had discussed escalating his rhetoric with his top advisers but used the phrase “fire and fury like the world has never seen” on his own accord.

The Washington Post and CNN reported that his remarks were improvised and not drafted by his team.

“General Kelly and others on the NSC team were well aware of the tone of the statement of the president prior to delivery,” Sanders said of Chief of Staff John Kelly and the National Security Council. “The words were his own. The tone and strength of the message were discussed beforehand.”