By CNN Pentagon Correspondent Barbara Starr
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WASHINGTON (CNN) -- Two U.S. government officials with access to classified information tell CNN that the initial air sampling over North Korea shows no indication of radioactive debris from the event Monday that North Korea says was an underground nuclear test.
The U.S. Air Force flew a WC-135 Constant Phoenix on Tuesday to collect air samples from the region.
A third official reiterated that at this point "there isn't information to allow confirmation it was a nuclear test."
The intelligence community and the military will continue to fly satellites and collect air samples in the region to try to collect radiological data that would provide confirmation of a nuclear test, officials said. But as time goes on, it will be increasingly difficult to achieve confirmation.
Officials emphasize this is preliminary data, and it provides no conclusive evidence about the North Korean event.
It is possible there was no radiological data. That could be the case if: the North Koreans successfully sealed the site; it was such a small detonation and so deep underground there was no escape of nuclear debris; or the test was actually conventional explosives.
Arms control monitors in Vienna, Austria, also tell CNN that they are now trying to run computer models to simulate wind conditions over the Korean Peninsula so they can try to calculate where radiological material might flow on air currents so they can position sensors for the best position to pick it up.
Government experts continue to emphasize they will continue to sample from air, ground and maritime sensors and they could get a positive reading.
One intelligence official said "lack of confirmation is not proof of a non-event."
The U.N. Security Council has agreed to vote Saturday on whether to impose sanctions on North Korea over its purported nuclear test, according to John Bolton, the U.S. ambassador to the United Nations. (Full story)
North Korean leader Kim Jong-Il