Speaking at an event in California yesterday, Mattis said his mission and responsibility was to have military options ready "should they be needed" but stressed the US effort is currently focused on diplomacy.
"The American effort is diplomatically led, it has diplomatic traction, it is gaining diplomatic results and I want to stay right there right now," Mattis said at an event in California.
"The tragedy of war is well-enough known it doesn't need another characterization beyond the fact that it would be catastrophic," he added.
Mattis did not elaborate on the diplomatic results he referenced, but the UN Security Council at the weekend passed a new set of sanctions against Pyongyang over its weapons program, including bans on the export of coal, iron and iron ore, lead and lead ore as well as fish and seafood.
In a diplomatic win for the United States, the measures were approved unanimously -- including by Russia and China, the North's sole major ally.