US officials told NBC News on Thursday that the US Air Force's special sniffer plane, known as a WC-135W Constant Phoenix, is capable of detecting evidence of a nuclear explosion.
The Air Force said in a statement that the aircraft "has been deployed on a routine mission to Northeast Asia. These missions are planned well in advance."
The statement said that the plane carries out about 150 missions in a year at a number of locations across the world, and "is designed to collect accurate information on levels of radiation in the atmosphere in order to monitor compliance with international treaties governing nuclear testing."
North Korea is capable of conducting a nuclear test with little or no warning, according to two American intelligence officials.
"We expect that they are able to do it at any time, without any real warning," one official said. "They have been engaging in steady preparations."
The officials refused to confirm or deny that the United States has detected signs that a nuclear test is imminent.
Posted by Amare Asrat