North Korea said Monday it conducted a ballistic missile launch drill the previous day that simulated a tactical nuclear counterattack, with the missile detonating 800 meters above the Sea of Japan.

The projectile, likely the single short-range ballistic missile detected by Japan and South Korea on Sunday morning, was equipped with a mock nuclear warhead, the official Korean Central News Agency said.

The missile test came amid the United States and South Korea conducting a joint military exercise dubbed "Freedom Shield," their first large-scale springtime joint drill in five years. The exercise runs through Thursday.

North Korea launches a ballistic missile in a drill on March 19, 2023, in Cholsan County, North Pyongan Province in the country's northwest. (KNS/Kyodo)

North Korean units in charge of operating tactical nuclear weapons conducted a combined drill on Saturday and Sunday, designed to familiarize them with the "procedures and processes for implementing" their attack missions, the report said.

The missile was launched from Cholsan County, North Pyongan Province in the country's northwest on Sunday and "accurately exploded 800 meters above the target waters" in its 800-kilometer strike range, "thus proving once again the reliability of nuclear explosion control devices," KCNA said.

The drill was personally overseen by leader Kim Jong Un, who, according to the report, stressed the need for service members to be "more perfectly prepared in their active posture for making an immediate and overwhelming nuclear counterattack anytime."

Kim also "set forth the important nuclear force-building orientation and the strategic tasks to be fulfilled in preparing the nuclear force for a war," KCNA said.

The leader was quoted as saying the country's "enemies are getting ever more pronounced in their moves for aggression," and that North Korea is urgently required to bolster "its nuclear war deterrence exponentially."

According to the Japanese government, the missile detected on Sunday is estimated to have flown about 800 km at a maximum altitude of around 50 km and may have flown on an irregular trajectory.

It is believed to have fallen into the Sea of Japan, outside Japan's exclusive economic zone.

Photos carried by state media showed Kim was accompanied by his daughter in overseeing the drill.

North Korean media also said more than 1.4 million young people in the country had newly signed up for military service as of Sunday in response to the U.S.-South Korea exercise, which Pyongyang views as an invasion rehearsal.

South Korea's Unification Ministry expressed Monday deep regret over North Korea's denunciation of the "defensive" drill conducted by Seoul and Washington while also saying Pyongyang is "posing threats with nuclear weapons in a hostile manner."

"It is clear that the cause and responsibility for creating the crisis on the Korean Peninsula lies in North Korea's reckless nuclear development," the ministry said.

South Korea and the United States embarked on their first large-scale amphibious landing exercise in five years on Monday, according to the South Korean military.

The Ssangyong training, held in and around the southeastern city of Pohang, will last until April 3. The last time such an exercise was held was in 2018, with former South Korean President Moon Jae In administration's efforts to improve inter-Korean relations the cause of the hiatus.

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