Japan's Defense Ministry says an undersea search has begun for an Air Self-Defense Force fighter jet that crashed off Aomori Prefecture on Tuesday.
Debris from the F-35A was found on Wednesday morning, but the pilot remains missing.
Defense Minister Takeshi Iwaya told reporters on Friday that aircraft and ships from the Self-Defense Forces, the Coast Guard and the US military are continuing their search.
He also said a submarine rescue ship of the Maritime Self-Defense Force began an undersea search on Friday morning.
The ministry plans to expand its fleet of F-35 jets to 147 over the next 10 years.
Iwaya said the ministry will focus on finding out the cause of the crash, and there has been no change to its deployment plan.
Referring to the two emergency landings that the fighter made in the past, he said faulty parts were changed before it was put back into service. He added that the ministry plans to investigate whether the repairs had anything to do with the crash.
Asked about concerns that China and Russia may try to recover the crashed jet, Iwaya said the ministry is monitoring foreign aircraft and vessels around the clock, and it has not detected any unusual activities.