U.S.: Test Points to N. Korea Nuke Blast

"The betting is that this was an attempt at a nuclear test that failed," a senior administration official said. "We don't think they were trying to fake a nuclear test, but it may have been a nuclear fizzle." The officials who described the results spoke on condition of anonymity because of the sensitive nature of the information.

North Korea's claim of a successful nuclear test Monday sent shock waves throughout Asia and around the world. President Bush has called for stiff United Nations sanctions on North Korea, while refusing appeals by U.N. Secretary-General Kofi Annan and others to take part in one-one-one talks with the reclusive communist regime.

Since North Korea's announcement, the United States and other nations have been conducting scientific tests to determine whether a nuclear explosion had occurred.

One congressional official said that radioactive material was found in an air sample collected on Wednesday.

The administration briefed key members of Congress about the preliminary test results. One official said the sample was collected above Qunggye, near the area of the claimed nuclear test.

Results from another test disclosed Friday _ an initial air sampling on Tuesday _ showed no evidence of radioactive particles that would be expected from a successful nuclear detonation, a U.S. government intelligence official said.

The contradictory readings reinforced uncertainty about the size and success of Monday's underground explosion, which North Korea has trumpeted as a nuclear test. Data from seismic sensors have already indicated the explosion was smaller than expected.

The Chinese and Japanese governments have done their own air sampling and found no trace of radioactive material, officials from both countries said Friday. A Japanese government official said his country sampled air over the Sea of Japan, as well as rainfall and ground-level air on Japanese territory and found nothing.

A spokesman for National Intelligence Director John Negroponte declined to comment on any findings from U.S. spy agencies.

One Republican lawmaker, citing the release of "intelligence reports appearing to confirm the likelihood of a North Korean nuclear test," backed Bush's call for international talks. But the lawmaker, Rep. Heather Wilson, R-N.M., also parted company with the president, saying that if a "prominent American delegation _ preferably a bipartisan one _ get North Korea to walk back from the ledge, we should do so."

The State Department, meanwhile, announced that Secretary of State Condoleezza Rice will travel to China, South Korea and Japan next week to discuss steps to pressure North Korea to drop its nuclear efforts and to assess the region's security situation.