(News Focus) N. Korea in advanced stages of miniaturizing nuke weapons: officials
SEOUL, Jan. 6 (Yonhap) -- North Korea is presumed to be in the advanced stages of miniaturizing nuclear bombs to be loadable onto ballistic missiles, possibly including hydrogen bombs, which the country claimed to have tested a day earlier.
North Korea announced that it has conducted its fourth nuclear test on Wednesday, apparently taking one step further toward its goal of developing nuclear weapon-fitted ballistic missiles.
The outside world, however, suspects that the detonation may not have been hydrogen-based because the explosive power registered from the Wednesday test was far too week for an H-bomb.
Whether it was a hydrogen bomb or an atomic bomb, South Korean government officials presumed on Thursday that North Korea may be in possession of nuclear weapons weighing about 4 tons, still too heavy to be carried by a ballistic missile.
The weapons need to be further downsized to 500-600 kilograms in order to be fitted onto a ballistic missile, the officials said.
According to some intelligence authorities, the North's quest for the smaller nuclear warhead is well under way.
"It is beyond our intelligence whether North Korea has developed a miniaturized hydrogen bomb, but it is still believed to have achieved much of the miniaturization technology itself, given the time the country has taken in its nuclear development so far," one intelligence official said.
The officials referred to recent progress in North Korea's high-explosive detonation tests as key evidence of the assessment.
Since the late 1980s, North Korea has conducted about 100 experiments of high-explosives, a vital nuclear weapon component whose detonation provides the initial force for an atomic blast, at a detonation testing ground in Pyongyang.
The average size of the bomb crater from the high-explosive experiment reached about 4 meters when intelligence officials first detected them in 1989, but the crater size shrank to the 1.5-m level in 2001 and further came down to 1 m afterward, the intelligence officials said.
Last year, North Korea did not conduct any related tests, according to South Korea's intelligence, an important sign that suggests the country has somewhat mastered the miniaturization technology.
Miniaturization is practically the final stage in the development of a nuclear warhead-tipped inter-continental ballistic missile.
The communist country may push ahead with one or two more nuclear tests down the road in order to secure smaller and lighter nuclear weapons, they said.
Still, Pyongyang seems far behind developing a hydrogen bomb, an official who represents the Defense Ministry said on condition of anonymity, calling into question the validity of North Korea's latest claim.
The Korea Meteorological Administration announced a 4.8-magnitude tremor was detected from North Korea's nuclear test site on Wednesday. A stronger 4.9-magnitude quake was registered from North Korea's third nuclear test in February 2013 when the country allegedly detonated a uranium-based nuclear bomb.
Given the intensity of the tremor registered on Wednesday, the test may not have been based on an H-bomb, which is far more destructive, experts and government officials have said.
But South Korea does not rule out the possibility of North Korea having conducted a test of a boosted fission bomb, which is usually more destructive than an atomic bomb, but less powerful than a hydrogen bomb.
"Even if it was a test of a boosted fission bomb, it must have been unsuccessful," the defense ministry official said.
"The destructive power of the Wednesday test reached 6 kilotons, it's far too weak for a hydrogen bomb," he said. As with a successful boosted fission bomb test, a destructive power that is two to five times stronger than that of the third test should have been registered, the official said, raising skepticism over the North's claim of a successful hydrogen bomb test.