Kim Jong Un said the recent launches were a clear warning to South Korea and the United States, informing them of North Korea's nuclear response posture and offensive capabilities. Kim has reiterated that he has no intention of resuming disarmament diplomacy with the United States at this time and will focus on expanding his arsenal.

According to state media reports, Kim Jong Un has indicated that North Korea's recent missile launches were tests of nuclear weapons capable of wiping out the US and South Korean military bases.

The North's statement, released on the 77th birthday of its ruling Worker's Party, is seen as an attempt to buttress public unity behind Kim as he faces pandemic-related economic hardships, a security threat posed by the boosted U.S.-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.

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

North Korea considers U.S.-South Korean military drills as an invasion rehearsal, although the allies have steadfastly said they are defensive in nature.

U.S. 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.

Kim Dong-yub, a professor at the University of North Korean Studies in Seoul, said North Korea aims to diversify its launch sites to make it difficult for adversaries to detect missile launches and launch preemptive strikes.

For example, a recent missile launch site was from an inland reservoir.

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 manoeuvrable KN-23 missile, which was modelled on Russia's Iskander missile.

Worries about North Korea's nuclear program deepened in recent months as the country adopted a new law authorizing the preemptive use of its bombs in certain cases and took reported steps to deploy tactical nuclear weapons along its frontline border with South Korea.

This year, North Korea has also carried out a record number of weapons tests with more than 40 ballistic and cruise missiles.

Some experts say Kim Jong Un would eventually aim to use his advanced nuclear arsenal to win the U.S. recognition of North Korea as a legitimate nuclear state, which Kim sees as essential in getting crippling U.N. Sanctions on his country lifted.