James Mattis has called upon the US army to be ready to respond to North Korea.
Speaking to the Association of the United States Army convention in Washington DC, he said the continued "provocations" of the secretive state were threatening "regional and global peace."
The US Secretary of Defense said a diplomatic-led and sanction-backed solution was being sought to persuade the country to disarm its nuclear weapons program.
However, he added the proviso the military needed to be ready to deploy as a military option available to Donald Trump.
This statement follows tweets posted by the US President, which said 25 years of agreements and money paid to North Korea had not solved the problem, saying "only one thing will work."
Trump did not clarify what that "one thing" was.
Both the comments made by the President and Mattis add to the growing tension between the US and North Korea, after the regime in Pyongyang announced its intention to continue with nuclear missile tests.