UNITED NEWS INTERNATIONAL (UNI) — A U.S. Air Force fighter jet crashed in the waters off Okinawa, leaving the pilot in serious condition.

According to U.S. defense officials, an F-15C fighter jet from Kadena Air Base crashed into the sea off the southern Japanese island on June 11.  

The unidentified pilot ejected and was rescued at sea by the Japan Air Self-Defense Force.

Officials said the aircraft “was conducting a routine training mission” when it crashed.

The cause of the crash is unknown, and the base said it has temporarily halted F-15 local training operations.

Monday’s incident marked the sixth non-combat crash for the U.S. Air Force in 2018, following seven last year.

The U.S. military presence on Okinawa has been a source of contention for local residents. Roughly half of the 50,000 American troops in Japan are stationed on the island.