Leader Kim Jong Un guided the launches and expressed his satisfaction with them, the North's official Korean Central News Agency reported, without saying when the tests happened.

The KCNA said the launches "once again examined the operational features of the detonating devices of nuclear warheads mounted on the ballistic rockets the designated altitude over the target area."

Lee Chun-geun, a scientist at South Korea's Science and Technology Policy Institute, said that the North Korean missiles were believed to be carrying warheads, which contain trigger devices but not plutonium or uranium, to see whether those warheads could detonate properly.

The launches were the latest in a series of weapons tests North Korea has carried out since Kim in March ordered tests of a nuclear warhead explosion and ballistic missiles capable of carrying such warheads.

Pyongyang said it conducted a similar test of a warhead-detonating device when it fired a submarine-launched missile in April.

North Korea is pushing to manufacture a warhead small enough to be placed on a long-range missile that can reach the continental US, but South Korean defense officials say the North doesn't yet have such a miniaturized warhead. Some civilian experts, however, believe the North has the technology to put warheads on shorter-range missiles that can strike South Korea and Japan.

The three reported launches came as North Korea loudly criticized the planned deployment of an advanced US missile defense system in South Korea. Seoul officials said all three missiles landed in the waters off the North's east coast.

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