The wreckage of the Japanese F-35 stealth fighter jet that disappeared from radar over the Pacific Ocean during a night training flight was found in the sea on Wednesday.
The Japanese defense ministry said the male pilot, who's in his 40s, remains missing.
The fighter jet went off the radar while flying off the eastern coast of Aomori, just about half an hour after taking off the Misawa air base with three other F-35As.
It remains unclear what caused the crash, Defense Minister Takeshi Iwaya told reporters, adding that 12 other F-35s at the base will be grounded.
"We have collected parts from the jet fighter's tail fin so we [believe] it crashed," Iwaya said, according to the BBC.
The U.S. military supported the Japanese allies in the search of the jet and the pilot. The U.S. Navy's 7th fleet, P-8A maritime patrol aircraft, and a guided-missile destroyer are continuing to assist Japanese-led search and rescue efforts for the pilot.
Some have warned that the crashed jet could have caused major security concern had the wreckage been first discovered by China or Russia, both of which long hoped to get their hands on the state-of-the-art military technology produced by the U.S.
Iwaya said that the pilot sent a signal to abort the mission, according to the broadcaster. Shortly after the signal, all communications with the fighter jet were lost.
Japanese military began deploying the U.S.-made F-35s since last year in an effort to ramp up defense spending amid threats from North Korea and China.
The government of Japan is also seeking to 147 F-35s, including 105 F-35As, costing about $90 million each.
Fox News' Lucas Tomlinson and the Associated Press contributed to this report.