Seoul, South Korea - North Korean leader Kim Jong Un oversaw a drill simulating a tactical nuclear attack, state media said Monday, as part of what Pyongyang described as a response to ongoing U.S.-South Korea joint military exercises.

The North Korean exercise, held Saturday and Sunday, included a "launching drill simulating a nuclear attack on major target of the enemy," according to the state-run Korean Central News Agency.

During the Sunday launching drill, a tactical ballistic missile with a mock nuclear warhead "correctly exploded in the air" at a height of 800 meters after traveling for 800 kilometers, KCNA added.

Analysts said the drill appeared aimed at simulating a nuclear airburst, the detonation of a warhead above ground to increase its effectiveness.

South Korea had earlier reported Sunday's launch, calling it at the time a short-range ballistic missile that was launched from the Tongchang-ri area of North Korea before splashing into the sea.

Kim, who was accompanied at the drill by his young daughter, said the maneuver was aimed at preparing North Korean nuclear forces to launch attacks "rapidly and correctly at any time and in any situation" to deter war, said KCNA.

North Korea held a similar tactical nuclear attack drill in October, when it fired a barrage of missiles it said were designed to "hit and wipe out" U.S. and South Korean targets.

In its report Monday, KCNA called the latest drills a response to U.S.-South Korea military exercises, which it said have been "frantically escalated."

The United States and South Korea on Thursday are set to wrap up 11 days of major joint military drills, including some of their largest field exercises in five years.

The two allies have also conducted more frequent drills involving U.S. "strategic assets," which refers to long-range bombers, nuclear-capable airplanes and aircraft carrier strike groups.

On Sunday, U.S. Air Force B-1B bombers participated in air drills with South Korean and U.S. fighter jets, according to South Korea's defense ministry. It was the eighth visit by a U.S. strategic bomber in the last four months.

Washington and Seoul say their military maneuvers are defensive - and point out they have only been ramped up after North Korea dramatically increased its own weapons tests and threats.

But North Korea says it views the U.S.-South Korea exercises as preparation to invade, and often uses the drills as an occasion to test some of its most powerful military equipment.

On Thursday, North Korea launched a Hwasong-17 intercontinental ballistic missile, which can potentially travel over 15,000 kilometers and reach anywhere on the U.S. mainland.

North Korea last year resumed long-range missile tests, after having paused them for several years during a period of diplomacy with the United States and South Korea.

However, most of North Korea's recent launches have involved tests of shorter-range missiles, like the one launched Sunday, which pose a major threat to South Korea.

North Korean state media photos of the launch showed a missile emerging from a mountainous area filled with two fiery orange plumes of smoke. No launcher was visible, leading analysts to conclude the missile was fired from a silo built into the mountain.

In recent years, North Korea has greatly diversified the platforms from which it can launch missiles. In recent months, North Korea has conducted launches from silos, trains, submarines, railcars, reservoirs, and mobile missile launchers.

Analysts say the strategy is meant to make it more difficult for U.S. and other intelligence agencies to monitor, predict, and detect North Korean launches.

North Korea says some of its newer short-range missiles can carry tactical nuclear weapons, which are generally designed for battlefield use and often have smaller explosive yields.

Over the past year, North Korea appears to have taken steps to deploy tactical nuclear weapons at frontline positions, analysts believe. North Korea last year also adopted a new law authorizing the preemptive use of nuclear weapons in certain situations.

In his comments published Monday, Kim hinted at the new approach, saying it is important for North Korean nuclear forces to be "perfectly prepared in their active posture of making an immediate and overwhelming nuclear counterattack anytime."