South Korean and U.S. officials said Sunday that a massive explosion that generated a billowing cloud of smoke on North Korea's northern border with China on Thursday was an unspecified accident and apparently not a much-feared nuclear test.
"We are investigating the size and the reason of the accident, but we do not believe North Korea conducted a nuclear test," said Kim Jong Min, the South Korean presidential spokesman.
Details of the blast remained sketchy. Some in U.S. intelligence circles had expressed increasing concern in recent weeks that North Korea was about to conduct a nuclear test, but South Korean officials said they did not record seismic activity that likely would accompany a nuclear test.
[According to a report posted on the BBC Web site early Monday, North Korea's foreign minister, Paek Nam Sun, told a visiting British official that the blast was caused by the deliberate demolition of a mountain as part of a hydroelectric project. That report could not be immediately verified.]
In Washington, U.S. officials scrambled Saturday night to gather more information about the blast and to study satellite photos of the site, but as dawn broke Sunday, Bush administration officials played down the significance of the explosion.
Making the rounds of the Sunday news shows, Secretary of State Colin L. Powell and national security adviser Condoleezza Rice said there was no indication that the blast was related to a nuclear test.
"We don't think, at this point, it was a nuclear event, but we're looking at it and will get further analysis," Rice said on CNN's "Late Edition." "There are all kinds of reports and all kinds of assessments that are going on. Maybe it was a fire, some kind of forest fire."
Powell acknowledged that the administration has been studying reports of suspicious activity at a possible nuclear test site, though officials have said the activity was at a different location than that of the explosion. "We're monitoring this," Powell said on ABC's "This Week." "We have been watching it. We can't tell whether it's normal maintenance activity or something more. So it's inconclusive at this moment."
Nevertheless, the date of the blast -- a day commemorating the 1948 founding of North Korea -- had U.S., South Korean and Japanese officials scrambling to determine what might have caused the huge explosion. North Korea is known to put great importance on historic dates, using them to conduct high-profile military exercises and parades.
One official in Washington said the Americans were examining satellite images of the explosion, which South Korea's semi-official Yonhap News Agency said generated a mushroom formation as large as 21/2 miles in diameter. The official said further information had been provided to the U.S. government by a diplomatic source in Beijing.
But the official said the explosion did not take place at the location that had been closely monitored in recent weeks by U.S. intelligence agencies. The surveillance was due to suspicious movement of vehicles that some analysts believed indicated preparation for a nuclear test.
The explosion -- reportedly larger than a chemical blast near a train station in North Korea in April that killed 150 people -- took place in the northern Yanggang province near the country's mountainous border with China, South Korean officials said.
In 1999, a South Korean presidential spokesman said in an interview that North Korea was building an underground ballistic missile launching facility in that region for the Taepodong-1, a missile that North Korea test-fired over Japan in 1998, and the longer-range Taepodong-2, which is believed to be in the final stages of development. Since then, some analysts have suspected that the heavily militarized and remote area may also house a new, intermediate North Korean missile with a range between 1,800 and 2,500 miles, and might additionally be a facility used for uranium reprocessing.
In December 2002, a missile engine test is suspected to have caused an explosion that destroyed facilities at North Korea's launching pad in Musudanri, North Hamkyong province, though it was quickly rebuilt for a successful test of the Taepodong-2's main engine last May, intelligence officials now contend.
Given the missile facilities in the area of Thursday's explosion, a South Korean official, who spoke on the condition of anonymity, said one working theory for the explosion was a possible missile-related accident. But the official stressed that intelligence was still too vague to provide a conclusive cause.
Staff writer Glenn Kessler in Washington and special correspondent Akiko Yamamoto in Tokyo contributed to this report.