North Korean leader Kim Jong Un oversaw a nuclear counterstrike drill involving a missile with a mock atomic warhead capable of reaching Japan’s west coast, its official media said.

Kim brought his daughter to exercises over the weekend, where he issued a threat to the U.S. over joint military drills it’s conducting with South Korea, saying his country is preparing to make "an immediate and overwhelming nuclear counterattack anytime,” the Korean Central News Agency reported Monday.

"The missile was tipped with a test warhead simulating a nuclear warhead,” KCNA said. The missile, fitted with detonators and devices to simulate a nuclear attack, exploded at a height of about 800 meters (875 yards) above its target, it said