Whether or not North Korea detonated a hydrogen bomb or just an atomic bomb -- there's a big difference in size and killing power -- many experts say that this week's test brings the rogue nation one step closer to putting a warhead on a ballistic missile, threatening its neighbors and perhaps the United States.
"They are getting better," said Kingston Reif, director for disarmament and Threat Reduction Policy at the Arms Control Association in Washington. "They are working toward this goal, and with each test they are making additional progress. The tests they just conducted last night contributed to their understanding and their capability."
North Korean officials said yesterday they had detonated a hydrogen bomb, a two-step thermonuclear device that uses energy released from the combination of two light atomic nuclei, while an atomic bomb uses the energy released when a heavy atomic nucleus splits, a process known as nuclear fission.
American scientists developed the hydrogen bomb, which was first tested in 1952.
However, White House officials today said they doubted North Korea's claim. They believe it was more likely an atomic bomb, similar in size to three previous ones tested by North Korea since 2006.
White House spokesman Josh Earnest said initial data from various monitoring sources were "not consistent with North Korean claims of a successful hydrogen bomb test."
Even so, many nuclear arms control experts say the test is worrisome.
"As for the rumor or claim of thermonuclear warhead, I doubt that seriously. The kind of seismic signature suggests something similar to a previous test," said Hans Kristensen, director of the Nuclear Information Project at the Federation of American Scientists. "That's not to say they are not working on it."
North Korea does have medium-range ballistic missile that can carry conventional weapons as far as South Korea and Japan, and is working on building intercontinental ballistic missiles (ICBMs) that could travel much farther, according to Reif.
The country has these missiles, but they aren't working yet, he said.
"North Korea does not currently deploy a ballistic missile with a range capable of reaching the United States," Reif said. "It has never tested a mobile ICBM, even though it has displayed it in mockups. It's not believed to be operational."
North Korea initially relied upon assistance from the Soviet Union and China to develop its arsenal, but it is now a chief exporter of ballistic missile systems and technology.
Even if North Korea can build a missile that can fly far enough to reach the West Coast of the United States, it also has to develop a re-entry vehicle to protect the nuclear warhead from the heat that builds up when it falls through the atmosphere on its way back down to its target.
"North Korea faces significant challenges in terms of fashioning a re-entry vehicle that would house a nuclear warhead on a missile," Reif said. "And conducting the kinds of tests to miniaturize a nuclear weapon to put on a missile."
According to Reif, the most reliable estimates are that North Korea could achieve a working ICBM by the early 2020s.