U.S. Waits for Firm Information On Nature and Success of Device

By Dafna Linzer and Thomas E. Ricks
Washington Post Staff Writers
Wednesday, October 11, 2006

The White House yesterday played down North Korea's nuclear capability as government scientists and intelligence analysts waited for additional data to confirm whether Pyongyang had conducted a successful nuclear test.

Intelligence and administration officials said they were still working under the assumption that North Korea had managed to detonate an atomic device, but they said they needed additional environmental sampling before they could formally rule out other possibilities, such as the blast being caused solely by conventional explosives. Intelligence officials were concerned that North Korea could conduct another test, either to improve upon the first test or to prove its capabilities.

A U.S. military RC-135, an electronic monitoring aircraft, flew around the Sea of Japan yesterday in an effort to detect nuclear radiation, two intelligence sources said. The same aircraft, based in Okinawa, Japan, was used in July after North Korea carried out a set of ballistic missile tests. The sources cautioned that it could take several days before winds push radioactive particles toward an area where they can be clearly detected.

"Over time, whenever the prevailing winds blow out over the Gulf of Japan, it will be more likely that we get some detection," one intelligence official said yesterday, requesting anonymity because the effort involves classified information.

Pentagon spokesman Bryan Whitman said officials would use a variety of means besides seismic data to try to draw a conclusion about the explosion, including some he would not discuss. "There is a possibility that particulate fallout is detectable, and then there's a variety of other intelligence means to determine the veracity of the allegation of the tests that they conducted," he said.

North Korea announced Monday that it had carried out its first nuclear test, and seismic readings suggested a blast inside a mountain in the country's north from the equivalent of 500 tons of explosives.

"We ourselves are operating under the assumption that, yes, in fact it was" a nuclear test, State Department spokesman Sean McCormack said yesterday. "But I can't confirm that."

The aircraft and monitoring stations on the ground are seeking to detect particulate data that would indicate that a nuclear explosion had taken place. But those efforts will not necessarily determine the nature of the blast, a Defense Department official noted, because the explosion was relatively small and the North Korean government said it was contained.

"There are multiple ways" the U.S. government will seek to verify North Korea's claim that it detonated a nuclear device, the official said. But there is no hard information yet, the official said. Intelligence analysts are also reviewing intercepted communications and other data.

The official declined to be quoted by name, saying that the Pentagon is not playing a lead role in the U.S. response and that he wanted to defer to the White House.

White House press secretary Tony Snow said there is a "remote possibility" that U.S. intelligence will be unable to fully determine whether the test succeeded. Several nuclear tests conducted by other countries, including a number of Pakistani tests in 1998, have never been fully understood by U.S. intelligence. Many intelligence analysts believe a 1979 flash in the waters off the southern tip of Africa was caused by a nuclear test carried out by Israel, with South African help. But it has never been confirmed and remains a mystery.

Snow suggested yesterday that it is possible that the test was conducted with an older weapon from before President Bush's time in office.

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