Amid speculations of an impending sixth nuclear test by North Korea, the U.S. Air Force has dispatched a nuclear sniffer aircraft that detects radioactive substances in the atmosphere.

A South Korean government source said the WC-135 Constant Phoenix, a special purpose U.S. aircraft, carried out an emergency mission over the East Sea on Thursday.

The source explained it appeared to be part of activities to prepare against a North Korean nuclear test.

The flight of the sniffer plane is believed to be based on projections of an imminent test by the regime or could be part of drills to test operational readiness for an actual mission in the case of a provocation. 

The Constant Phoenix arrived at Kadena Air Base in Okinawa, Japan on April seventh.