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South Korea's nuclear agency said Saturday it is still seeking confirmation of whether a North Korean weapon test was nuclear, despite US findings showing consistencies with an atomic blast.
South Korea's government-affiliated Korea Institute of Nuclear Safety would not comment on the US findings, released Friday, that indicate a sample of air taken after Monday's test contained radioactive debris consistent with an atomic explosion.
The agency is currently studying seawater samples collected off South Korea's east coast to seek separate signs of abnormal radioactivity from North Korea, institute official Han Seung-jae said. Results are expected next week.
South Korean monitoring has so far detected no abnormal levels of radioactivity in South Korean air or rainwater, but officials have cautioned the findings do not indicate North Korea did not conduct a nuclear test or that a nuclear test had failed.
A US government official, who spoke on condition of anonymity, cautioned that the administration has not made a definitive conclusion about the nature of the explosion.
"The betting is that this was an attempt at a nuclear test that failed," the official said. "We don't think they were trying to fake a nuclear test, but it may have been a nuclear fizzle - an effort that failed." The official spoke on condition of anonymity because of the sensitive nature of the information.
The official said the test measures a type of gas. It is one of a number of analyses conducted this week, which have not provided clarity about what North Korea detonated on Monday.
The air sample was taken Tuesday by a specialized aircraft, the WC-135, flying from Kadena air base in Okinawa, Japan. It apparently took the sample over the Sea of Japan, between the Korean mainland and Japan.
In Beijing, a government official said Friday that Chinese monitoring also has found no evidence of airborne radiation from the test-explosion. The official with the State Environmental Protection Administration said China has been monitoring air samples since Monday.
The US intelligence official said an initial result from the US air sample testing became available late this week. He said a final result would be available within days but the initial finding is considered conclusive.
It was not immediately clear whether the WC-135 took additional samples after the Tuesday effort.