The pilot of a Lockheed Martin F-35A stealth fighter jet that crashed into the Pacific Ocean called an end to his training exercise just before the plane went down, it was learned Wednesday.

Japan's Defense Ministry has launched an investigation to determine the cause of Tuesday's crash, which will be carried out by the ministry's aircraft accident investigation commission. The Japan Air Self-Defense Force has requested the U.S. military's cooperation for the probe as well.

"I want to work toward preventing a recurrence as the investigation committee looks into the cause," Defense Minister Takeshi Iwaya told reporters.

The downed jet was one of four F-35A planes to take off from Misawa Air Base in Aomori Prefecture at about 7 p.m. Tuesday. It vanished from the JASDF's radar about 135 kilometers from the base over the Pacific after roughly 25 minutes. Iwaya confirmed earlier Wednesday that the aircraft had crashed.

The condition of the pilot, a major in his 40s with approximately 3,200 hours of flight time, including 60 hours in the F-35A, was unclear. The investigation committee will question the other three pilots who were involved in the training exercise.

This was the first time an F-35A had crashed anywhere in the world, according to the defense ministry. Japan grounded its other 12 fighters after the crash. The move will have no impact on its air defenses, however, because those planes were only deployed for training purposes.

The jets began to arrive at Misawa from January last year. The crashed aircraft was the first delivered plane, which was assembled at a Mitsubishi Heavy Industries facility in Aichi Prefecture from U.S. components.

Japan has gradually procured more F-35s, which the government considers its main next-generation fighter jet, as a replacement for the difficult-to-repair F-15.