North Korea says its launch of two ballistic missiles on Wednesday night was a tactical nuclear strike drill to protest a combined air exercise over the Korean Peninsula held earlier in the day involving a U.S. B-1B strategic bomber.

The North’s state-run Korean Central News Agency on Thursday quoted the North’s General Staff as saying that by conducting the combined air exercise, Seoul and Washington have unveiled to the world their intention to launch preemptive nuclear attacks against the North.

The General Staff claimed that in response, the tactical nuclear-armed unit of the Korean People’s Army carried out a drill on Wednesday with tactical ballistic missiles to simulate scenarios on wiping out key command strongholds and airfields of the South’s military.

The General Staff said the projectiles were launched from Pyongyang International Airport and accurately detonated at a preset altitude of 400 meters above a target island.