Secretary of Defense James Mattis made his first on-camera remarks Thursday about North Korea's threats to attack Guam with ICBMs, saying that a potential nuclear incident "would be catastrophic."

While speaking to reporters at the Defense Innovation Unit Experimental(DIUx) event in Mountain View, California, he was asked by a reporter, "Can you talk about the human toll we might see in the event of a nuclear confrontation?"

"My portfolio, my mission, my responsibility is to have military options if you need it,” Mattis responded. "However, right now, Secretary Tillerson, Ambassador Haley, you can see the American effort is diplomatically led, it has diplomatic traction, it is gaining diplomatic results. And I want to stay right there right now. The tragedy of war is well enough known. It does not need another characterization beyond the fact that it would be catastrophic."

Deviating from the tone of President Trump, who said the U.S. would unleash "fire and fury" upon North Korea, Mattis stressed that the route forward would be diplomatic, and he repeated the importance of the unanimous 15-1 United Nations Security Council vote to impose economic sanctions on North Korea.

"It’s [North Korea's] aligning the United Nations in very serious sanctions, and I would just tell you that it did not happen by accident," Mattis said. "That shows where the Trump administration goes in terms of the prioritizing of the threat but also how to deal with it in a diplomatically effective manner."

Reporter asks Defense Sec. Mattis about "human toll" of possible nuclear confrontation. "It would be catastrophic." https://t.co/zZOhvmKxje pic.twitter.com/YVQwDQLMNy — ABC News (@ABC) August 11, 2017

And Mattis said earlier in a statement, "While our State Department is making every effort to resolve this global threat through diplomatic means, it must be noted that the combined allied militaries now possess the most precise, rehearsed and robust defensive...capabilities on Earth,” Mattis said in a statement.

Mattis’ comments come on the heels of North Korea’s state media announcement Thursday that its military would devise a plan by mid-August to fire four intermediate range missiles at the U.S. territory of Guam as a “crucial warning to the U.S.”

Trump has notched up his criticism of North Korean leader Kim Jong-un, saying he has “gotten away with [horrific] things for a long time between him and his family” and that he wouldn't let Jong-un “get away it” now. Trump added that “maybe the statement wasn’t tough enough” and that North Korea can expect a reaction “of the likes of which nobody has seen before” if Jong-un strikes Guam.

ABC News' Elizabeth McLaughlin contributed to this report