The North’s statement, released on the 77th birthday of its ruling Workers’ Party, is seen as an attempt to buttress a public unity behind Kim as he faces pandemic-related economic hardships, a security threat posed by the boosted US-South Korean military alliance and other difficulties.

"Through seven times of launching drills of the tactical nuclear operation units, the actual war capabilities… of the nuclear combat forces ready to hit and wipe out the set objects at any location and any time were displayed to the full," the North’s official Korean Central News Agency said.

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KCNA said the missile tests were in response to recent naval drills between US and South Korean forces, which involved the nuclear-powered aircraft carrier USS Ronald Reagan for the first time in five years.

Viewing the drills as a military threat, North Korea decided to stage "the simulation of an actual war” to check and improve its war deterrence and send a warning to its enemies, KCNA said.

Kim Jong Un monitors a North Korean missile launch at an undisclosed location. File/AFP

North Korea considers US-South Korean military drills as an invasion rehearsal, though the allies have steadfastly said they are defensive in nature. Since the May inauguration of a conservative government in Seoul, the US and South Korean militaries have been expanding their exercises, which had been previously scaled back due to the pandemic and the now-dormant nuclear diplomacy between Pyongyang and Washington.

The launches — all supervised by Kim — included a nuclear-capable ballistic missile launched under a reservoir in the northeast; other ballistic missiles designed to strike South Korean airfields, ports and command facilities; and a new-type ground-to-ground ballistic missile that flew over Japan, KCNA reported.

North Korea has previously test-launched missiles from a submarine off its east coast. But the most recent was its first public test of a weapon from under an inland reservoir.

Kim Dong-yub, a professor at Seoul’s University of North Korean Studies, said North Korea likely aims to diversify launch sites to make it difficult for its enemies to detect its missile liftoffs in advance and conduct preemptive strikes.

North Korean leader Kim Jong Un (centre) in white, inspects military exercises in North Korea. File/AP

KCNA said when the weapon launched from the reservoir was flying above the sea target, North Korean authorities confirmed the reliability of the explosion of the missile’s warhead, apparently a dummy one, at the set altitude.

Kim, the professor, said the missile’s estimated 600-kilometre (370-mile) flight indicated the launch could be a test of exploding a nuclear weapon above South Korea’s southeastern port city of Busan, where the Reagan previously docked. He said the missile tested appeared to be a new version of North Korea’s highly maneuverable KN-23 missile, which was modeled on Russia’s Iskander missile.

North Korea described the missile that flew over Japan as a new-type intermediate-range weapon that traveled 4,500 kilometers (2,800 miles). Some foreign experts earlier said North Korea likely tested its existing nuclear-capable Hwasong-12 missile, which can reach the US Pacific territory of Guam. But Kim, the professor, said the missile appeared to be an improved version of the Hwasong-12 with a faraway target like Alaska or Hawaii.

Associated Press