North Korea (search) said Monday that an explosion last week that raised a huge mushroom cloud was the planned demolition of a mountain for a hydroelectric project, and the reclusive government invited a British diplomat to visit the site to confirm the story.
The North's explanation came as a number of officials and experts from the United States and elsewhere said they dixplosion and concerns over Pyongyang's nuclear ambitions set off a heated back-and-forth between the White House and Democratic rival John Kerry (search).
North Korea denounced the speculation over a nuclear test as part of a "smear campaign" against it, aimed at diverting world attention away from new revelations about past South Korean nuclear activities.
Speaking on the condition of anonymity, a U.S. official said it isn't clear what happened. While the official said there isn't any reason to believe it was a nuclear test, the official also couldn't confirm the North Koreans explanation that it was linked to the construction of a hydroelectric project.
A U.N. official, who asked for anonymity, said the Comprehensive Nuclear-Test-Ban Treaty Organization (search) — a U.N. body that monitors explosions worldwide for signs of nuclear activity through an international network of sensing devices — had not picked any signs that the explosion was a nuclear blast.
The North's official news agency KCNA explained the explosion saying "blastings at construction sites of hydro-power stations in the north of Korea" had taken place.
North Korean Foreign Minister Paek Nam Sun told the same to visiting British Foreign Office minister Bill Rammell.
In an interview with the British Broadcasting Corp., Rammell said Paek told him the blast "wasn't an accident, that it wasn't a nuclear explosion, that it was a deliberate detonation of a mountain as part of a hydroelectric project."
Rammell welcomed the explanation and said that the North Koreans "have nothing to fear and nothing to hide and should welcome the international community actually verifying the situation for themselves."
North Korea told Britain's ambassador in Pyongyang, David Slinn, that he can visit the blast site as soon as Tuesday to verify its claims, the Press Association of Britain reported.
South Korean Unification Minister Chung Dong-young said his country would look into "whether that area is an area for constructing a hydroelectric power plant," according to the news agency Yonhap.
Andrew Kennedy, head of the Asia program at the Royal United Services Institute in London, said the North Korean explanation has "a ring of truth to it" and that if diplomats allowed to the site take a Geiger counter with them they would easily know whether a nuclear blast occurred.
"The North Koreans would know that with the intelligence and the surveillance satellites that the West has, it would be very easy to check. That is backed up by the North's agreement to allow the visiting British diplomat to go to the site and inspect it," he said Monday.
"North Korea is usually trying to convince people that they do have a nuclear capability. ... It's not in their interest to keep a nuclear test quiet," he added.
There was no comment from the International Atomic Energy Agency (search), whose inspectors were told to leave North Korea after it quit the Nonproliferation Treaty last year.
The size of the reported explosion on the 56th anniversary of the founding of North Korea had raised speculation that it might be a nuclear test. Secretary of State Colin Powell said Sunday there was no indication the blast was from a test.
Kerry, the Democratic president candidate, said that just the idea that the United States was thinking North Korea might test a nuclear weapon highlights a national security failure by Bush. Under Bush's watch, North Korea has advanced its nuclear program, he said.
"North Korea's nuclear program is well ahead of what Saddam Hussein was even suspected of doing — yet the president took his eye off the ball, wrongly ignoring this growing danger," Kerry said in a statement. "What is unfolding in North Korea is exactly the kind of disaster that it is an American president's solemn duty to prevent."
In a telephone call Sunday evening to The New York Times, Kerry accused the administration of letting "a nuclear nightmare" develop by refusing to deal with North Korea when it first came to office, the paper reported on its Internet site.
Responding to the Times story, Bush spokesman Scott McClellan accused Kerry of wanting to return to "the failed Clinton administration policy" on North Korea. He said that while Clinton's 1994 agreement with North Korea calling for a freeze fell apart, Bush is trying to rally North Korea's neighbors to pressure the country to abandon its nuclear activities.
"That failed policy let North Korea dupe the united States. It would be the wrong approach to go down that road again," McClellan said.
The North's KCNA news agency denounced the speculation of a test as "a preposterous smear campaign" and a "fabrication intended to divert elsewhere the world public attention focused on the nuclear-related issue of South Korea for which they are now finding themselves in a dire fix."
IAEA chief Mohamed ElBaradei (search) on Monday chided South Korea, expressing "strong concern" that Seoul had not informed the agency of its nuclear activities. He revealed that Seoul produced more than 300 pounds of uranium metal in the 1980s at three secret facilities.
It then used some of that metal in nuclear enrichment experiments using laser technology conducted in 2000.
Diplomats said the use of the metals developed earlier raised doubts over Seoul's explanation that the 2000 experiments were carried out by a group of renegade scientists without government authorization.
The revelations have complicated efforts to persuade the North to give up its nuclear weapons ambitions. On Saturday, North Korea said the South's activity made the communist state more determined to pursue its own nuclear programs.