Pyongyang regularly criticizes such drills as rehearsals for invasion and sometimes responds with weapons tests, but Seoul and Washington say they are purely defensive.

North Korean leader Kim Jong Un stressed his order of a quick expansion of his forces' nuclear capabilities, citing the annual U.S.-South Korea military exercises, according to the country's state media.

North Korea leader Kim Jong Un said his country needed to rapidly expand its nuclear armament and called U.S.-South Korea military exercises an "obvious expression of their will to provoke war," state media KCNA reported on Tuesday.