The United States is preparing a preemptive attack on North Korea — and they want Kim Jong Un to know it.

National security adviser H.R. McMaster told MSNBC that the United States military was preparing all options to stop the reclusive communist country's nuclear ambitions.

When asked what extra preparations President Donald Trump was preparing, McMaster cut to the chase. "What you're asking is are we preparing plans for a preventive war, right?" McMaster said in response to host Hugh Hewitt's questions. "A war that would prevent North Korea from threatening the United States with a nuclear weapon. And the president's been very clear about it. He said he's not gonna tolerate North Korea being able to threaten the United States. If they have nuclear weapons that can threaten the United States. It's intolerable from the president's perspective. So of course, we have to provide all options to do that. And that includes a military option."

McMaster's statement is a clear warning to Kim Jong Un — back off, or we'll take out down.

The reclusive dictator didn't seem phased. North Korea vowed Monday to bolster its nuclear arsenal and gain revenge of a "thousand-fold" against the United States in response to tough U.N. sanctions imposed following its recent intercontinental ballistic missile tests.

The statement came two days after the U.N. Security Council unanimously approved new sanctions to punish North Korea, including a ban on coal and other exports worth over $1 billion. The U.S. ambassador to the U.N., Nikki Haley, called the U.S.-drafted resolution "the single largest economic sanctions package ever leveled against" North Korea.

In a statement carried by the North's state-run Korean Central News Agency, North Korea's government said the sanctions were a "violent infringement of its sovereignty" that was caused by a "heinous U.S. plot to isolate and stifle" North Korea.

"We will make the U.S. pay by a thousand-fold for all the heinous crimes it commits against the state and people of this country," the statement said.

The North said it would take an unspecified "resolute action of justice" and would never place its nuclear program on the negotiating table or "flinch an inch" from its push to strengthen its nuclear deterrence as long as U.S. hostility against North Korea persists.

North Korean Foreign Minister Ri Yong-ho made similar comments during an annual regional security conference in Manila on Monday.