North Korea has the ability to put a nuclear warhead onto a medium-range missile and threaten its regional neighbors, especially Japan, some U.S. experts believe.

With North Korea preparing to return to six-party talks on its nuclear program, scientists and other analysts stress that few facts are known about the reclusive country’s capabilities and conclusions depend largely on circumstantial evidence.

U.S. intelligence officials say there is no evidence that North Korea has physically “mated” a warhead to a medium-range Rodong missile, let alone has nuclear-armed Rodongs ready for launch. Some officials believe Pyongyang has yet to meet the engineering challenge of arming a missile.

But word that the North Koreans tested a relatively small nuclear device on October 9 is bolstering assertions that Pyongyang has moved directly to a warhead for its medium-range arsenal.

“We’ve assessed that North Korea can put a warhead on a Rodong,” said physicist David Albright, who heads the Institute for Science and International Security in Washington.

“What you’re trying to do is reduce the diameter to fit inside a re-entry vehicle. You can do that with a crude nuclear weapons design,” he added.

John Pike, director of the Alexandria, Virginia, online think tank GlobalSecurity.org, agrees.

“I have never been able to understand why there would be any doubt about North Korea’s capacity to put a nuclear weapon on a medium-range ballistic missile. They’ve had it for several years,” Pike said.

The Rodong has a range of 870 miles, which could hit most of Japan and all of South Korea.

Richard Garwin of the IBM Research Center and Princeton professor Frank von Hippel also suggest North Korea could be aiming for a warhead small enough for the Rodong or even its shorter-range Scud missiles.

MISSILE SPECULATION

Until recently, speculation about Pyongyang’s nuclear ambitions has concentrated on the long-range multi-stage Taepodong-2 missile, which analysts believe could some day be capable of reaching the U.S. mainland.

But the Taepodong-2 exploded just after launch during its first test flight on July 5.

Pyongyang would most likely use nuclear-tipped Rodongs to threaten Japan as a means of deterring any U.S. military action against North Korea, experts say.

“Even if there’s only a 10 percent probability that they’ve produced a few warheads and put them on Rodong missiles, that could still be enough to deter the United States because the possible effect on Japan is catastrophic,” said Daniel Pinkston, Korea expert at the Monterey, California-based Center for Nonproliferation Studies.

But some experts say Pyongyang would be unlikely to use nuclear weapons against fellow Koreans in the South.

Conservative estimates suggest North Korea, which has more than 200 Rodongs and over 600 Scuds, has enough fissile material for six to eight nuclear weapons, though some analysts say the number could top one-dozen.

U.S. intelligence determined over a decade ago that Pyongyang was trying to develop a warhead for its medium-range arsenal but had yet to overcome the engineering obstacles.

Albright and Pike said those hurdles appear now to have been surpassed.

North Korea would have to conduct test a Rodong with a simulated warhead, before deploying a credible medium-range nuclear threat, U.S. intelligence officials said.

Albright and Pike said Pyongyang may have done just that on July 5, when it test-fired seven missiles including Rodongs.