"A US Navy salvage team aboard a contracted vessel completed its mission supporting search and recovery operations with the Japan Self-Defense Forces," the US 7th Fleet said in a statement on Wednesday.

Japan will continue searching for the remains of the plane, a defence spokesman said.

Some debris has already been recovered from the high-tech F-35A that plummeted into the sea off the coast of northeastern Japan on April 9.

But the "all-important" memory that could offer clues into the accidents has not been recovered, and the jet's pilot has also not been found.

Experts say Japan and the US are keen to prevent debris from the plane being recovered by Russia or China, with Japan's Defence Minister Takeshi Iwaya admitting last month there were "a significant amount of secrets that need to be protected" on board.

The fighter jet went missing on April 9 while flying 135 kilometres (85 miles) east of Misawa, northeastern Japan, on a training mission.

The plane lost contact about 30 minutes after taking off from Misawa Air Base with three other aircraft.

It was the first reported case of a crash by an F35-A, according to Japan's Air Self-Defence Force.

Japan is deploying F35-As, each of which costs more than 10 billion yen ($90 million), to replace its ageing F-4 fighters.

They are a key part of Prime Minister Shinzo Abe's efforts to upgrade the nation's military capacity to meet changing power dynamics in East Asia, with China rapidly modernising its military.