In this file photo taken on Dec. 18, 2019, U.S. Defense Secretary Mark Esper participates in a press conference at the State Department in Washington, DC. AFP

U.S. Defense Secretary Mark Esper on Thursday urged North Korean leader Kim Jong-un to exercise "restraint" after the communist nation threatened to reveal a "new strategic weapon" in protest over stalled nuclear talks.

Kim made the remark in a New Year's message that expressed his frustration over stalled denuclearization talks with the U.S. Experts have said the "strategic weapon" Kim said the world will see in the near future could be an intercontinental ballistic missile.

"We would urge restraint by Kim Jong-un," Esper said in an interview with Fox News, noting that the best path forward is still a political agreement on denuclearizing North Korea.

"We are on that path. We want to remain on that path, and we would obviously urge Kim Jong-un and his leadership team to sit back down at the negotiation table to do that," he said.

Esper made clear, however, that the U.S. military stands ready to "fight tonight" if necessary.

"We have a full array of forces. They are ready. They're Air and Naval, Marine, Army forces. We have our South Korean partners with us, and then we have a broader set of allies and partners out there as well," he said. "So I'm confident in the readiness of our forces to deter North Korean bad behavior and should that fail, to fight and win as necessary."

Speaking to reporters at the Pentagon, Esper also said the U.S. has been monitoring the situation very closely but would not say whether there have been indications of an imminent test or launch.

"I obviously don't talk about intelligence matters," he said.

Pressed to respond to Kim's threat to showcase a new strategic weapon, Joint Chiefs of Staff Chairman Gen. Mark Milley weighed in, "We'll see what happens.

"Our military defensive capabilities are adequate to defend the homeland." he added.