WASHINGTON -- Although US spy satellites have detected what may be preparations for North Korea's first test of a nuclear weapon, a US defense official said yesterday that analysts believe it could be a calculated ruse on Pyongyang's part.
The satellite images show North Korea has dug and refilled a significant hole at a suspected test site in Gilju in the northeastern part of the country, said the official, discussing intelligence only on the condition of anonymity.
The hole was dug in a manner consistent with preparations for an underground nuclear test, but it is not known whether the North Koreans deposited a weapon inside, the official said. In addition, the official said, they have built some bleachers a sufficient distance from the hole, presumably for viewing any test.
Officials elsewhere in the US government played down the developments. One who spoke on condition of anonymity said activity at the site could be consistent with preparations for a nuclear test, but other explanations also are possible.
The official said the US government's working assumption is that North Korea could test with little notice and is believed to have the technical capability to do so. Its decision on whether to test is considered to be one of politics.
Presidential spokesman Scott McClellan said he did not want to get into discussing intelligence matters. ''But what I would say is that if North Korea did take such a step, that would just be another provocative act that would further isolate it from the international community."
''All countries in the region are committed to seeing a nuclear-free peninsula," McClellan said aboard Air Force One as President Bush traveled on the first leg of a five-day, four-country visit to Central and Eastern Europe.
At the State Department, spokesman Tom Casey said, ''We don't have any new assessment" of North Korea. Casey said various North Korean statements had raised concerns and the United States was sharing them with other governments.
Although North Korea has claimed that it has nuclear weapons, an actual test would be a first and confirm their capabilities to the world. US intelligence and other estimates put the number of their weapons between one and six, so using one in a test would reduce their inventory by a significant amount.
But the North Koreans also have a good idea when US spy satellites are overhead -- the United States does not possess enough to watch the country constantly -- and are capable of making such preparations solely to cause a reaction among its adversaries, the defense official said.
Separately, a senior Japanese Defense Agency official said Japan's government had information that North Korea might be preparing for a nuclear test.
Japan yesterday threatened to put the issue of North Korea's nuclear weapons program before the UN Security Council next month unless six-nation talks on the dispute show progress.
The New York Times reported yesterday the US government has told Japan and South Korea about the satellite imagery. Tuesday, South Korea's mass-circulation Chosun Ilbo said US satellite photos showed frequent movement of trucks and placement of cranes and other equipment in the North Korean town Gilju.