A search-and-rescue operation is underway for a U.S. Marine Corps pilot who ejected from his F/A-18 aircraft today off the coast of Japan during a scheduled training mission.

The pilot ejected at about 4:40 a.m. ET, 120 miles southeast of Iwakuni, Japan, according to a news release from Marine Corps Base Camp Butler in Okinawa.

The F/A-18 was assigned to the 1st Marine Aircraft Wing in Okinawa and was conducting "regularly scheduled training at the time of the mishap," Marine Corps Base Camp Butler said.

The cause of the incident is under investigation, and the Marine Corps did not provide further information.

Another F/A-18 fighter that was flying with the one that went down remained in the area until it had to leave because it was running out of fuel.

Capt. Jeff Davis, a Pentagon spokesman, said a number of U.S. and Japanese air and surface assets are involved in search-and-rescue efforts.

Three Japanese ships are also assisting as are multiple Japanese fixed wing and rotary wing aircraft.