"Today (Monday), the combined Japanese and United States teams... had a breakthrough when their surface ships and dive teams were able to locate remains along with the main fuselage of the aircraft wreckage," the US Air Force said in a statement.

"The dive teams were able to confirm five additional crew members from the original team of eight that were involved with the crash," it said.

"Currently two crew members of the five located today have been successfully recovered by the attending teams. There is an ongoing combined effort to recover the remaining crew members from the wreckage."

Hours after the aircraft disappeared on November 29 near the island of Yakushima, Japanese first responders had located and recovered the first known casualty from the crash of the CV-22 aircraft.

The latest discovery, which follows a large-scale joint search operation that has lasted since the incident, meant that two crew members from the aircraft remained unaccounted for.

Japan's public broadcaster NHK, citing unidentified sources, said earlier on Monday what appeared to be the front part of the aircraft, possibly including the cockpit, had been found.

The Osprey, which can operate like a helicopter or a fixed-wing turboprop plane, has suffered a string of fatal accidents.

A crash in northern Australia killed three US Marines in August, while four more died in another crash in Norway during NATO training exercises last year.

Three Marines were also killed in 2017 when another Osprey crashed off Australia's north coast and 19 Marines died when their Osprey crashed during drills in Arizona in 2000.

- Suspension request -

The United States temporarily grounded the aircraft in Japan in 2016 after an Osprey crash-landed off Okinawa, sparking anger among locals.

Defence Minister Minoru Kihara said on Thursday he had asked the US military to again suspend Osprey flights -- except for search-and-rescue operations -- and that Japan's military had halted using its own Ospreys pending safety checks.

But the Pentagon announced that only the unit of the crashed CV-22 had halted flying.

"The United States is taking all appropriate safety measures, as we do for every flight and every operation," spokeswoman Sabrina Singh said last week.

"The unit of the CV-22 that had the accident is not conducting flight operations. All V22 Ospreys in Japan operate only after undergoing thorough maintenance and safety checks," Singh said.

"We have already started sharing information about the accident with our Japanese partners, and have pledged to continue to do so in a timely and transparent manner."

An emergency management official in the Kagoshima region where the crash took place said police had been told the aircraft had been "spewing fire from a left engine".

NHK quoted a local fisherwoman who said she saw the aircraft crash into the sea, sending up a column of water 100 metres (330 feet) into the air.