An air sampling taken after North Korea's claimed nuclear test detected radioactive debris consistent with an atomic explosion, U.S. officials said Friday night — but other tests found no trace of such particles.

The White House and U.S. congressional officials, who were in Washington, said no final determination had been made about the nature of last weekend's mystery-shrouded underground blast.

One congressional official said that radioactive material was found in an air sample collected on Wednesday. But results from another test disclosed Friday — an initial air sampling performed Tuesday — showed no evidence of radioactive particles that would be expected from a successful nuclear detonation, a U.S. government intelligence official said.

The Chinese and Japanese governments have done their own air sampling and also found no trace of radioactive material, officials from both countries said Friday.

"The betting is that this was an attempt at a nuclear test that failed," said a senior official from White House. "We don't think they were trying to fake a nuclear test, but it may have been a nuclear fizzle."

The U.S. officials who described the results spoke on condition of anonymity because of the sensitive nature of the information.

North Korea's claim on Monday that it had successfully carried out a nuclear test a day earlier sent shockwaves throughout Asia and around the world.

U.S. President George W. Bush called for stiff United Nations sanctions on North Korea, while refusing appeals by UN 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. Data from seismic sensors have already indicated the explosion was smaller than expected.

A Japanese government official said Friday his country sampled air over the Sea of Japan, as well as rainfall and ground-level air on Japanese territory and found nothing.

UN Security Council to vote on sanctions

Members of the UN Security Council agreed Friday on wording of a resolution that would clamp sanctions on North Korea.

The draft, scheduled for a Saturday vote, would authorize nonmilitary sanctions against the country, and says that any further action the council might want to take would require another UN resolution.

It also eliminates a blanket arms embargo from a tougher, previous draft, instead targeting specific equipment for sanctions including missiles, tanks, warships and combat aircraft.

U.S. State Department spokesman Sean McCormack said that on Rice's trip, "she's going to be talking about the passage of that resolution certainly, but really what comes after."

Rice to travel to China, S. Korea, Japan

The U.S. 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.

Rice's trip is meant to present a unified front to North Korea, which will be looking for any cracks in the diplomatic coalition behind the UN statement.

Coming less than a month before midterm congressional elections, Rice's trip is also an opportunity for the Bush administration to highlight its work countering what it considers to be dangerous regimes and terrorist threats.

Beyond the threat to Asian neighbors and perhaps other nations posed by a nuclear North Korea, the administration is worried that Pyongyang could sell its nuclear know-how to terrorists or other potential U.S. enemies, including Iran.