The issue of North Korea's nuclear weapons capability has returned to the spotlight as US Forces Korea Commander Curtis Scaparrotti said last Friday that the communist state was thought to have the capability to miniaturize a nuclear warhead.
"I believe (North Koreans) have the capability to miniaturize a device at this point, and they have the technology to potentially deliver what they say they have," he said during a press briefing at the Pentagon.
"We have not seen it tested. And I don't think as a commander we can afford the luxury of believing perhaps they haven't gotten there."
Although Pyongyang conducted nuclear tests in 2006, 2009 and last year, some experts and officials here have said that it remains unclear whether the North has reached a technological level to make nuclear warheads small enough to mount on ballistic missiles.
Last month, Seoul's Defence Ministry spokesman Kim Min-seok said that it was "senseless" to think that Pyongyang succeeded in developing tactical nuclear weapons, while noting that Seoul does not believe that the North has developed a nuclear warhead that weighs less than 1 ton.
To mount a nuclear warhead on its SCUD-B missile with a range of 300 km, the North should reduce its weight to less than 1 ton and its diameter to 90 centimeters, experts say.
In June, Kim also played down Pyongyang's nuclear capability, saying that it was meaningless for the North to produce nuclear warheads that are not miniaturized. His statement came shortly after the Stockholm International Peace Research Institute said in its Yearbook 2014 that the North appeared to have six to eight nuclear warheads.
Amid the rekindled controversy over the North's nuclear weapons, Pentagon Press Secretary Rear Adm. John Kirby said that the North was still "ways away" from developing a nuclear-capable intercontinental ballistic missile.
"He (Scaparrotti) didn't say that they (North Korea) have the capability to put a nuclear weapon on an ICBM. He said he believes they have the capability to miniaturize ― to get to that. But they have not moved ― we have not seen evidence that they have done it," Kirby told reporters.
"That is not the same thing as saying that they have the capability to mount, test and deliver a nuclear weapon on an ICBM. The difference is the ability to get the material into a state that it could be weaponized, but it is not that they are at that point right now."
To produce warheads mountable on long-range missiles, their miniaturization remains a critical task for the North. Since 1980, the North is presumed to have conducted more than 100 experimental high-explosive detonations as well as the two nuclear tests, all of which have helped it gradually enhance its miniaturization technology.
Kim Tae-woo, a nuclear politics expert at Seoul's Dongguk University, said it is wrong to judge that the North is still far away from miniaturizing its nuclear warheads.
"It is only natural (to judge that the North has the miniaturization capability) given that it has conducted as many as three nuclear tests. It is wrong to say that the North is still far away from that capability," he said.
Kim said that the North might prioritize developing nuclear warheads mountable on Scud missiles with a range of 300-500 km or on Rodong missiles that can travel some 1,300 km, given that missiles with too short ranges could affect its own territory, while the missiles with ranges of several thousand kilometers could provoke neighbouring states such as China and Japan.
But he said that the North could develop a warhead for an ICBM to bargain in its negotiations with the US