Kadena Air Base has paused all F-15 Eagle flying operations after a pilot crashed in the early hours Monday morning off the coast of Okinawa, the base said Monday.

The F-15C, assigned to the 44th Fighter Squadron of the 18th Wing, crashed at approximately 6:26 a.m. The lone pilot "successfully ejected" and was rescued by Japan Air Self-Defense Force, but remains in serious condition after being transferred to the U.S. Naval Hospital, Kadena officials said.

The pilot of the fourth-generation aircraft was conducting a routine training flight when the crash occurred over the southern waters of Okinawa.

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"I would like to personally thank the Naha Rescue Squadron for their quick response this morning, which led to the safe recovery of our airman," said Col. Richard Tanner, 18th Wing vice commander, in a statement. "I sincerely appreciate the strong support of our Japanese partners in this difficult situation."

Officials said the cause of the accident is unknown. The Air Force has launched an investigation following the accident.

The crash is the latest in a rash of Air Force aircraft mishaps in recent months.

As of May 2, manned aviation Class A mishaps have increased 48 percent in fiscal 2018 over the previous year, according to Air Force data. Class A mishaps involve fatalities, severe damage totaling $2 million or more, or a complete loss of the aircraft.

So far this year, the Air Force has lost six aircraft in non-combat training accidents, including a HH-60 Pave Hawk helicopter, T-38 Talon trainer, WC-130 Hurricane Hunter, two F-16 Fighting Falcons -- one being from the Thunderbirds demonstration team -- and the Kadena-based F-15. Several of the mishaps have included fatalities.

In March, a portion of the Air National Guard's F-15 Eagle fleet at Kingsley Field, Oregon, was grounded over significant maintenance issues affecting the aircraft's structure.

-- Oriana Pawlyk can be reached at oriana.pawlyk@military.com. Follow her on Twitter at @oriana0214.