Two Chinese SU-30 aircraft carried out what the U.S. military described on Thursday as an "unprofessional" intercept of a U.S. aircraft designed to detect radiation while it was flying in international airspace over the East China Sea.

"The issue is being addressed with China through appropriate diplomatic and military channels," said Air Force spokeswoman Lieutenant Colonel Lori Hodge.

Hodge said the U.S. characterization of the incident was based on initial reports from the U.S. aircrew aboard the WC-135 Constant Phoenix aircraft "due to the maneuvers by the Chinese pilot, as well as the speeds and proximity of both aircraft."

"Distances always have a bearing on how we characterize interactions," Hodge said, adding a U.S. military investigation into the intercept was underway.