Pentagon chief Jim Mattis on Thursday slammed North Korea's test launch of an intercontinental ballistic missile as a "provocation," but stressed the United States seeks a diplomatic solution to the standoff.

"As (Winston) Churchill put it, better to jaw-jaw than war-war. We (are) right now dealing with this very serious escalation, this provocation, this affront to the United Nations Security Council resolutions," Mattis said in his first public comments since Tuesday's test.

"We remain in a diplomatic effort engaging allies and partner nations across the board."