U.S. Defense Secretary Ash Carter and his South Korean counterpart, Han Min Koo, warned North Korea that any aggression or military provocation by the isolated regime "is not to be tolerated."
Carter and Han met Monday in Seoul in an annual review of their nearly five-decade old military alliance. In a joint statement, the duo pledged to "work shoulder-to-shoulder to demonstrate our combined resolve." They also expressed "grave concern" about Pyongyang's recent vows to carry out another long-range missile test or a fourth nuclear test.
The defense chiefs also signed an agreement that would transfer wartime operational control of South Korean forces from the United States back to Seoul when it improves its military and intelligence capabilities, including its counter-artillery operations against North Korea.
The two sides first agreed to transfer control back as early as 2007, but it was postponed several times after increased tensions on the peninsula, including the sinking of the South Korean warship Cheonan that was blamed on Pyongyang.
The new agreement signed Monday pushes that timetable to sometime after 2020.
Carter later Monday traveled to Malaysia for a meeting of defense ministers from the Southeast Asian region.