The pilot of a U.S. F-15C fighter jet was hospitalized in serious condition after it crashed Monday in waters south of Okinawa in southern Japan, the Air Force said.

The pilot, who was not identified, ejected and was rescued by the Japan Air Self-Defense Force.

The cause of the 6:30 a.m. crash is under investigation, the Air Force said. It said the F-15C from Kadena Air Base in Okinawa was on a routine training mission.

The heavy U.S. military presence in Okinawa has been the source of friction with the local government and some residents. About half of the 50,000 American troops in Japan are stationed on the southern island.

(AP)