The Pentagon describes these forthcoming moves as the “enhanced deployment of U.S. strategic assets in and around South Korea on a rotational basis,” but it has provided few additional details. It appears they are still in the works. Marine Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, said in an interview Saturday he had just discussed the deployment of strategic assets with South Korean counterparts during two days of meetings in Seoul.

“Is it different things? No,” Dunford said. “Is it doing different things at different times? Yes. And is it incorporating other capabilities on occasion? Yes.”

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Dunford declined to detail what might be used, but said the discussion centered on combining the 28,500 U.S. troops based in South Korea full time along with annual exercises and “our occasional rotation of forces” to bolster deterrence against North Korea. The point, he said, is to demonstrate the strength in the alliance between South Korea and the United States and the capability to respond militarily if necessary.

“It wasn’t a specific, ‘We want this or that,’ ” Dunford said of the message the South Koreans conveyed. “It was more of a conversation about exercise cycles, patterns of deployments and so forth that would most enhance.”

Defense Secretary Jim Mattis has been even more vague. Asked Saturday at a news conference in Seoul if strategic assets will stay on the South Korean Peninsula for a fixed amount of time, he declined to answer.

“Regarding our strategic assets, they are global in their positioning,” he said. “They are global in their reach, and we are quite assured that they are in a position to be responsive . . . So, that’s all I’ve got to say about that.”

Mattis’s South Korean counterpart, Defense Minister Song Young-moo, said the two countries have agreed to expand “relevant cooperation” involving strategic assets, including studies to improve deterrence against North Korea.

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Song also asked last month for the United States to consider reintroducing tactical nuclear weapons in South Korea, but the move is considered unlikely among many U.S. military officials. In addition to it potentially putting tensions with North Korea at a new high, Moon has said he is against the idea.

Dunford spent the weekend here in Hawaii following his meetings in Seoul for a three-party gathering that again included his South Korean counterpart, Gen. Jeong Kyeong-Doo, along with their Japanese equivalent, Adm. Katsutoshi Kawano.

South Korea and Japan have had strained relations for years, dating back at least to the Empire of Japan’s occupation of the Korean Peninsula during World War II and its use of so-called “comfort women,” who were forced into sexual slavery for Japanese soldiers. The three nations have participated together in operations meant to be a unified message for North Korean leader Kim Jong Un.

In one example, Air Force B-1B bombers from Andersen Air Force base in Guam flew in formation Sept. 17 with fighters from all three nations before dropping live bombs on a range few dozen miles from the demilitarized zone separating the two Koreas. The Japanese F-2 fighters broke off from the formation and did not fly over the peninsula, but were depicted in photographs released by the Pentagon in a show of force.

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The U.S. Navy typically keeps the movements of its submarines secret, but it also has periodically sent them to port in South Korea. The USS Michigan, an Ohio-class nuclear-powered submarine, has appeared at Busan Naval Base in South Korea at least twice this year. It is capable of carrying cruise missiles and elite Navy SEALs, although not ballistic missiles.

More recently, the Navy announced last week it has plans for a massive exercise involving three aircraft carriers — the USS Nimitz, the USS Theodore Roosevelt and the USS Ronald Reagan — and their associated strike groups, each of which include dozens of aircraft and thousands of sailors and Marines.

The exercise will be carried out as Trump visits South Korea, and is a rarity — no three-carrier operation has occurred since 2007, said Marine Lt. Gen. Kenneth F. McKenzie Jr., the director of the Pentagon’s Joint Staff. Dunford and others have effectively downplayed the significance of the timing as a coincidence, citing the length of time it takes to plan the movements of aircraft carriers.

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“These three carriers are not there specifically targeting North Korea,” the chairman said. “This is a routine demonstration of our commitment to the region.”

The chairman did acknowledge closer attention is being paid to Pyongyang, in light of its actions.

“I think it’s fair to say that all of us,” he said, “have a heightened sense of urgency for the past year and a half, and in particular, in the last couple months.”