“We are focused on modernizing our alliance with both the Republic of Korea and Japan, transforming these critical alliances to meet the challenges of the 21st century,” Mr. Mattis said, using South Korea’s formal name.
He also said the United States would continue to support Taiwan, the self-governing island that China claims as its territory, with military and other assistance.
Aaron L. Friedberg, a professor of politics and international affairs at Princeton University and a former deputy assistant for national security affairs, said that Mr. Mattis’s speech was probably meant to ease American allies’ concerns not just about regional threats, but about President Trump’s oft-changing foreign policy.
“They don’t know what’s coming next,” Mr. Friedberg said. “There’s not much people even at Mattis’s levels can do about it.”
Mr. Mattis said little about North Korea in his speech, which came just hours after Mr. Trump said that the June 12 talks in Singapore with the North’s leader, Kim Jong-un, were back on. He said the American goal remained the “irreversible denuclearization of the Korean Peninsula.” In response to a question, he added that American troop levels in South Korea would not be on the agenda for the summit talks.