Mattis made the comment during his week long trip in Asia.
With the South Korean Defense Minister by his side, Mattis accused North Korea of illegal and unnecessary missile and nuclear programs, and vowed to defeat any attack.
"Any use of nuclear weapons by the north will be met with a massive military response, effective and overwhelming," Mattis stated.
Mattis is visiting the region ahead of the president, who is expected to touch down in South Korea early next month in what the administration is calling a "good faith effort"
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