Air Force and Navy officials said they had taken the step "to mitigate risk while the investigation continues".

Not all of the remains of service members killed in the crash have been recovered yet.

Japan grounded its fleet of 14 Ospreys after the crash as well.

Japan is the only other nation known to operate Ospreys, which operate both as a helicopter and an aircraft with a propeller.

The Air Force said the American fleet is expected to remain grounded until it completes its investigation. It did not say how long that might take.

"The stand down will provide time and space for a thorough investigation to determine causal factors and recommendations to ensure the Air Force CV-22 fleet returns to flight operations," Air Force Special Operations Command said in a statement on Wednesday.

At the time of the crash, the Osprey had been on a training flight from a US Marine Corps air base in Yamaguchi Prefecture and was headed towards Kadena Air Base in Okinawa.

Eyewitnesses said the aircraft flipped over and was on fire before crashing offshore.

Six bodies have been found of the eight killed in the crash.

"The honourable service of these eight Airmen to this great Nation will never be forgotten, as they are now among the giants who shape our history," said Lt Gen Tony Bauernfeind, the commander of Air Force Special Operations Command.

The Osprey - a vehicle designed to take off and land like a helicopter but speed forward like a fixed-wing aircraft - is used by the US Air Force, Navy and Marine Corps. Over 400 are currently in service.

First introduced in 2007 after decades of testing, Ospreys have come under scrutiny for being involved in multiple fatal accidents during its time in service.

More than 50 service members have died either on Osprey flight tests or training flights.

In August, a separate model of Osprey crashed during a military exercise in Australia, killing three US Marines and injuring 20 others. The incident is still under investigation.

Another crash involving an Osprey in the California desert last year caused the deaths of five Marines.

Earlier this year, the Navy, Air Force, and Marines grounded some V-22 Ospreys due to an ongoing issue with the tiltrotor's hard clutch.