U.S. defense secretaries have long offered assurances to South Korea and Japan that its nuclear "umbrella" will protect them, but Mattis's statement was perhaps more pointed than most. He made the remarks during an appearance with his South Korean counterpart, Defense Minister Han Min Koo.
"North Korea continues to launch missiles, develop its nuclear weapons program, and engage in threatening rhetoric and behavior," Mattis said with Han standing at his side and U.S. and South Korean flags at their backs.
"We stand with our peace-loving Republic of Korea ally to maintain stability on the peninsula and in the region," he added. "America's commitments to defending our allies and to upholding our extended deterrence guarantees remain ironclad: Any attack on the United States, or our allies, will be defeated, and any use of nuclear weapons would be met with a response that would be effective and overwhelming."