If North Korea follows through on its latest threat of setting off a nuclear explosion over the Pacific Ocean, it will ultimately be up to President Trump whether the United States will respond with military action, Secretary of State Rex Tillerson told ABC News today.

ABC News Anchor David Muir asked Tillerson in an interview on “Good Morning America” about North Korea’s warning that it could detonate a hydrogen bomb over the Pacific in response to Trump’s speech to the United Nations General Assembly this week.

“If we see this detonation of an H-bomb in the Pacific, what will the U.S. do?” Muir asked. “Will there be military action?”

“That will be the president’s decision,” Tillerson said. “There is assembled on a standing basis a National Security Council that meets on each of these issues to advise the president. Ultimately it will be his decision.”

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The secretary of state defended Trump’s blunt rhetoric in his speech to the U.N. General Assembly in New York on Tuesday, in which the president threatened to “totally destroy” North Korea if the United States is “forced to defend itself or its allies,” prompting astonished gasps from some in the audience. Trump also mocked North Korean leader Kim Jong Un in the speech, dubbing him “Rocket Man.”

Kim responded in a statement Thursday saying Trump will “pay dearly” for his address to the U.N. and that North Korea is considering the strongest possible response to what he called the U.S. president’s provocation.

North Korean Foreign Minister Ri Yong-ho, in New York for the U.N. General Assembly, said Thursday evening that his country could detonate a hydrogen bomb over the Pacific Ocean, but also told reporters, “We have no idea about what actions could be taken as it will be ordered by leader Kim Jong Un.”

Trump responded to Kim’s threats on Twitter on Friday morning, calling him a “madman” who “will be tested like never before.”

Muir asked Tillerson about the “escalating rhetoric … does it work?”

Tillerson said, “The president obviously takes the responsibility of the security of the American people very seriously.”

“But we’re not in this alone,” he added. “We have developed strong allies and strong alliances internationally.”

“We are engaging with North Korea’s most important supporters, economic supporters, their friends, China and Russia, to have them also engage with Kim Jong Un on this issue,” he said.