N. Korea blast wasn't nuclear, South decides

SEOUL -- Was that a mushroom cloud that the satellite saw hovering menacingly over North Korea or merely a patch of bad weather?

Trying to end one of the more bizarre episodes in the standoff over North Korea's nuclear program, South Korea's deputy unification minister, Rhee Bong Jo, said yesterday that ''a closer inspection of the cloud suggests that it was a natural phenomenon."

The cloud -- as well as an unexplained tremor measuring about magnitude 2.6 -- was detected Sept. 9, the anniversary of the communist nation's founding. The coincidence of the phenomena on such a symbolic date fueled speculation about a nuclear test.

The South Koreans say the tremor appears to have come from the area around Mount Paekdu, a dormant volcano straddling the Chinese border, and was probably a natural movement, unrelated to the cloud, spotted about 60 miles away over Kim Hyong Jik County.

Making matters more confusing, the North Koreans have offered a different explanation: The tremor was caused by a series of explosions to level a mountainside as part of a construction project for a hydroelectric dam.

A delegation of European diplomats was taken Thursday to the construction site in the North Korean town of Sansu and allowed to take photographs and samples. South Korean officials say the hydroelectric project is too far from where the tremor or cloud were detected to be related, but the diplomats appear to think otherwise.

Bush administration officials have suggested that North Korean leader Kim Jong Il might pull an ''October surprise" and test a nuclear weapon in the coming weeks in an effort to influence the US presidential election.

''It would obviously not be smart for the North Koreans to test," national security adviser Condoleezza Rice said Sunday on CNN's ''Late Edition," after reports of the explosion. ''The North Koreans would only succeed in isolating themselves further."

Many analysts took the view that a nuclear test is unlikely at this time. ''There is a lot of fear-mongering going on about North Korea right now, but I think the probability of a test is very low," said Daniel Pinkston of the Center for Nonproliferation Studies in Monterey, Calif. ''If they tested, they would only confirm what the US already believes -- that they have nuclear weapons -- and they would use their small stock of fissile material."

Diplomats here believe, however, that the misleading report of a mysterious explosion was more likely an honest error on the part of South Korean intelligence.

For its part, North Korea has accused South Korea of spreading the rumor of a nuclear test in order to distract from its own woes. The International Atomic Energy Agency, the UN nuclear watchdog, is investigating alleged violations of the Nuclear Nonproliferation Treaty by South Korean scientists since the early 1980s.