North Korean leader says will soon conduct nuclear, missile tests

North Korean leader Kim Jong Un said his country would soon conduct a nuclear warhead test and a test launch of ballistic missiles capable of carrying nuclear warheads, the North's official KCNA news agency reported on Tuesday.

Kim made the comments as he supervised a successful simulated test of atmospheric re-entry of a ballistic missile that measured the "thermodynamic structural stability of newly developed heat-resisting materials", KCNA said.

"Declaring that 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 to further enhance the reliance of nuclear attack capability, he (Kim) instructed the relevant section to make prearrangement for them to the last detail," the agency said.

South Korea's defence ministry said there were no indications of activities at the North's nuclear test site or its long-range rocket station, but that North Korea continues to maintain readiness to conduct nuclear tests.

South Korean President Park Geun-hye said the North would lead itself to self-destruction if it did not change and continued the confrontation with the international community.

The North's report comes amid heightened tension on the Korean peninsula as South Korean and U.S. troops stage annual military exercises that Seoul has described as the largest ever.

In the apparent re-entry simulation, the official newspaper of North Korea's ruling Workers' Party carried pictures on Tuesday of a dome-shaped object placed under what appeared to be a rocket engine and being blasted with flaming exhaust. In separate images, Kim observed the object described by KCNA as a warhead tip.

The North has issued belligerent statements almost daily since coming under a new U.N. resolution adopted this month to tighten sanctions against it after a nuclear test in January and the launch of a long-range rocket last month.

"What would be terrible is if the DPRK (North Korea) re-enacted Operation Frigate Bird or the fourth Chinese nuclear test and did a two-in-one," said Jeffrey Lewis of the California-based Middlebury Institute of International Studies.

"For now, though, it looks like a nuclear test and several missile tests in close succession," he said.

In 1962, the United States launched a ballistic missile with a live warhead in what was known as the Frigate Bird test. China conducted a similar test in 1966.