SEOUL • North Korean leader Kim Jong Un said his country has successfully miniaturised a thermonuclear warhead and ordered improvements in the power and precision of its arsenal.
While the North has boasted of mastering miniaturisation before, this is the first time Mr 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, carried in the state media yesterday, came a day after the North's powerful National Defence Commission threatened pre-emptive nuclear attacks on South Korea and the US mainland, as Seoul and Washington kicked off their largest-ever joint military exercises.
"The nuclear warheads have been standardised to be fit for ballistic missiles by miniaturising them," Mr Kim noted during a visit with nuclear technicians. This can be called a true nuclear deterrent," he was quoted as saying.
Mr Kim also stressed that the miniaturised warheads were "thermonuclear" devices, echoing the North's claim that the nuclear test it conducted in January was of a more powerful hydrogen bomb.
This can be called a true nuclear deterrent.
MR KIM JONG UN, during a visit with nuclear technicians, on the miniaturised warheads.
The North Korean ruling party's newspaper, Rodong Sinmun, carried a large front-page picture of Mr Kim standing in front of what some experts said would appear to be a sized-down device.
South Korea's Defence Ministry said after the release of the images that it did not believe the North has successfully miniaturised a nuclear warhead or deployed a functioning inter-continental ballistic missile.
Ms Melissa Hanham, an expert at the Middlebury Institute of International Studies in California, said Pyongyang's nuclear scheme had been running long enough, with enough tests, to make it "distinctly possible" that effective miniaturisation had been achieved.
"I don't know that they could target that missile very well, or what its range might be, but the claim cannot be dismissed as bluster," she said.
The miniaturisation issue is key because, while North Korea is known to have a small stockpile of nuclear weapons, its ability to deliver them accurately to a target on the tip of a ballistic missile has been a subject of heated debate.
Most experts rule out the prospect of North Korea launching any sort of nuclear strike with a largely untested system, saying it would be tantamount to suicide given overwhelming US technical superiority.
Tensions have surged since the North carried out its fourth nuclear test in January and a long-range rocket launch last month.
In a sign of increased urgency to calm the situation, Chinese Foreign Minister Wang Yi said on Tuesday that China is open to reducing the number of participants in the six-party talks aimed at persuading the North to give up its nuclear weapons programme. China has always insisted that all six parties should be involved in any resumption of the nuclear talks.
Mr Wang held a telephone conversation with US Secretary of State John Kerry on the issue yesterday and will be making a two-day trip to Russia, a member of the stalled six-way talks.
AGENCE FRANCE-PRESSE, REUTERS