North Korea threatens to test nuclear warhead

Kim Jong Un warned of the impending tests on Tuesday, saying they served "to further enhance the reliance of nuclear attack capability," according to the Korean Central News Agency (KCNA).

Kim made the announcement as he monitored a simulated test of a warhead re-entry vehicle needed to guide a rocket safely back into the Earth's atmosphere. It would need such technology to strike the US mainland.

But Seoul's Defense Ministry is skeptical of the claim, and says intelligence suggests its northern neighbor hasn't yet developed such sophisticated re-entry technology.

According to KCNA, Kim said "a nuclear warhead explosion test and a test-fire of several kinds of ballistic rockets able to carry nuclear warheads will be conducted in a short time."

"He instructed the relevant section to make pre-arrangement for them to the last detail," KCNA said, but did not specify when the tests might take place.

Barrage of threats

In the past, the North has carried out nuclear tests every three to four years. Most recently, it tested a nuclear device in January and fired a long-range rocket in February, prompting the UN Security Council to impose its strictest sanctions ever on the secretive state.

The latest rhetoric from Pyongyang comes at a time of heightened tensions on the Korean peninsula. For the past several days, South Korean and US forces have been carrying out annual joint military drills in the area. The North sees the maneuvers - said to be the largest ever conducted by the two allies - as preparations for an invasion. In response it's issued a string of nuclear strike threats.

Even if the tests mentioned in Tuesday's report go ahead, analysts in Seoul say the nuclear warhead explosion will likely be just a test of an empty warhead - containing only a trigger device but lacking plutonium or uranium. They also say the North is still years away from developing a missile that could hit inter-continental targets.

Pyongyang said last week it had succeeded in developing the technology to fit a nuclear warhead on a missile. Seoul also disputes that claim.