Some of the parts belonging to a missing Japanese F-35 stealth fighter jet that crashed into the Pacific Ocean during a training flight have been recovered, the country’s defense ministry announced Wednesday, as a U.S. guided-missile destroyer joined in on the frantic search for the rest of the aircraft and its pilot.

The U.S.-made plane vanished from radar Tuesday night shortly after taking off from the Misawa air base with three other F-35As – and experts have warned the loss of the jet could become a major security headache if Russia or China get their hands on the wreckage first.

Japan’s Air Self-Defense Force said parts of the jet were found late Tuesday, but the rest of it and its pilot – whom officials say is a man in his 40s – are still missing. It’s also not clear yet what caused the aircraft to plunge into the water.

The U.S. Navy’s guided-missile destroyer USS Stethem and a P-8A maritime patrol aircraft are assisting in search and rescue efforts for the missing plane, which authorities say disappeared around 85 miles east of the base.

Japan started deploying the expensive F-35s last year as part of its plan to bolster defense spending and weapons capability to counter potential threats from North Korea and China. The 12 other F-35s at the Misawa base will be grounded as the search continues, Defense Minister Takeshi Iwaya said.

Under guidelines approved in December, Prime Minister Shinzo Abe's government plans to buy 147 F-35s, including 105 F-35As, costing about $90 million each.

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Rome-based aviation expert, pilot, and former Italian Air Force officer David Cenciotti told Fox News on Tuesday that if Russia or China find the aircraft first, “it could present problems depending on what is recovered, when it is recovered and, above all, in which conditions, after impacting the surface of the water."

“The F-35 is a system of systems and its low observability/stealthiness is a system itself,” he added.

Fox News’ James Rogers and the Associated Press contributed to this report.