"We've seen reports of this explosion, but based on the information we have, it was not any kind of nuclear event," Powell said in an interview on the television program Fox News Sunday.

"We're trying to find out more about it and what exactly it was, if anything, but it does not appear to have been a nuclear event," he said.

According to South Korea's Yonhap news agency, a huge explosion rocked North Korea's northern inland province of Ryanggang last week, triggering a mushroom-shaped cloud near a secret underground military base.

South Korean officials said the blast was not likely linked to a nuclear test and officials in Vladivostok, a Russian city located near where the blast occurred, said radiation levels were stable on the day of the explosion.

Speaking to CNN television, President George W. Bush's National Security Adviser Condoleezza Rice said the United States was seeking "further analysis" of what occurred in North Korea.

"There are all kinds of reports and there are all kinds of assessments that are going on, maybe it was a fire of some kind, a forest fire of some kind," she said. "But we don't believe at this point that it was a nuclear event."

Powell also commented on a report in the New York Times that US officials had received conflicting intelligence reports in recent days indicating North Korea may be preparing to conduct its first nuclear weapon test.

"With respect to reports in the paper this morning that there is activity going on at a potential nuclear test site, we are monitoring this," Powell said.

"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, but we continue to monitor these things very carefully," he said.

Speaking of a nuclear test, Powell said "the North Koreans know that this would not be a sensible step for them to take, and it is not just the reaction that they might see in the United States. It's their own neighbors.

"I think their neighbors would view such tests with great alarm," he said.

Speaking on NBC television's "Meet the Press," Powell called for the denuclearization of the Korean Peninsula.

"What we have to do is denuclearize the Korean Peninsula, for sure, in a verifiable way that leaves no question that the Peninsula has been denuclearized," he said, adding that this meant both "North and South (Korea)."

He reiterated US concern with North Korea's efforts to develop a nuclear capability.

"We are concerned about all of North Korea's nuclear development activities," Powell said on ABC television's "This Week." "That's why we have engaged all of North Korea's neighbors in the six-party framework talks.

"As North Korea makes these provocative statements, and if they take any provocative action, it's not going to be something that's just going to be of interest to the United States; it's going to be of interest to China, to Russia and Japan.

"So we're into a very intense period of negotiations. These things take time. And we'll see where it will lead," he said. "But, you know, it's no longer just North Korea versus the United States. It's North Korea versus all of its neighbors, which have no interest in seeing North Korea with a nuclear weapon."

Rice stressed that the United States was seeking to resolve the nuclear crisis with North Korea through diplomatic means.

"The president never rules out options, but I want to emphasize this is something that we believe can be dealt with diplomatically," she said.

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