Mattis threatens 'overwhelming' response if North Korea ever uses nukes
His remarks came on his first overseas trip to South Korea, where he met with his counterpart in the Republic of Korea's Ministry of Defense and other government officials.
"North Korea continues to launch missiles, develop its nuclear weapons program and engage in threatening rhetoric and behavior," Mattis said. "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."
He also praised South Korea - which has nearly 30,000 US troops stationed there - as a "lynchpin of peace and stability" in the Asia-Pacific region.
Mattis' stern warning to the North is likely to be taken seriously, since Pyongyang often responds to the slightest provocation. For example, North Korea regularly threatens total war against its southern neighbor whenever the US and South Korean forces train together during annual exercises, which are regularly scheduled and known well ahead of time.
The secretary's overseas trip was also another chance to push the South to continue with its deployment of the US's powerful THAAD missile defense system, which would blanket the country with protection from conventional or nuclear-tipped missiles fired from the north.