North Korean leader Kim Jong-Un said his country has successfully miniaturized a thermo-nuclear warhead.

North Korean leader Kim Jong-Un said his country has successfully miniaturized a thermo-nuclear warhead, as Pyongyang on Wednesday continued to talk up its nuclear strike capabilities amid rising military tensions on the Korean peninsula.

While the North has boasted of mastering miniaturization before, this is the first time Kim has directly claimed the breakthrough that experts see as a game-changing step towards a credible North Korean nuclear threat to the US mainland.

His comments came a day after the North's powerful National Defense Commission threatened pre-emptive nuclear attacks on South Korea and the US mainland, as Seoul and Washington kicked off large-scale joint military exercises.

Military tensions have surged in the region since the North carried out its fourth nuclear test in January and a long-range rocket launch last month.

The UN Security Council responded by imposing tough new sanctions last week, which Pyongyang has condemned and labeled as part of a US-led conspiracy to bring down Kim's regime by force.

"The nuclear warheads have been standardized to be fit for ballistic missiles by miniaturizing them," Kim noted during a visit with nuclear technicians that was reported by state media on Wednesday.

"This can be called a true nuclear deterrent," he was quoted as saying.
Kim also stressed that the miniaturized warheads were "thermo-nuclear" devices, echoing the North's claim that the nuclear test it conducted in January was of a more powerful hydrogen bomb.

The North Korean ruling party's newspaper, Rodong Sinmun, carried a large front-page picture of Kim standing in front of what some experts said would appear to be a sized-down device.