North Korea says it has miniaturized nuclear warheads
Under a UN Security Council resolution, North Korea is banned from developing any ballistic-missile technology.
Kim also inspected the nuclear warheads designed for thermo-nuclear reaction, KCNA said, referring to a hydrogen bomb that the country claimed to have tested in January.
North Korea conducted its fourth nuclear test on January 6 and claimed it was a hydrogen bomb test, which was disputed by many experts and the governments of South Korea and the United States.
The UN Security Council imposed harsh new sanctions on the isolated state last week for the nuclear test, and Pyongyang has stepped up its belligerent rhetoric through state media.
Last week Kim ordered his country to be ready to use nuclear weapons at any time in the face of growing threats from enemies.