The crash did not kill anyone and only caused injuries to two of the five crew members aboard the US Marine MV-22 Osprey.

The Pentagon described the December 2016 crash as a "mishap", which saw the plane end up in shallow water off Okinawa.

But Japanese coast guard officials on Tuesday referred the case to prosecutors on suspicion that the pilot had been flying too fast, causing the crash, a coast guard spokesman said.

Under the terms of the Japan-US Status of Forces Accord that governs the presence of US troops in the country, Japan can indict US military personnel accused of crimes in the country.

But Japanese courts do not have automatic jurisdiction to hear the cases.

The coast guard spokesman said the pilot has not been identified by US forces, and that the American military has so far not cooperated with the investigation into the accident.

The incident sparked anger on Okinawa, a strategic outpost of US military power, which hosts more than half of the 47,000 American military personnel in Japan.

The military presence is a sensitive subject on the island, where many feel other parts of Japan should share the burden of hosting US personnel.

The incident also came at a delicate time, with Tokyo and Washington pushing to build a new airbase on Okinawa despite local opposition.

The MV-22 Osprey, a so-called tilt-rotor plane, is half helicopter, half turboprop with the manoeuvrability of a chopper and the speed and range of a fixed-wing aircraft.

But a series of accidents involving the plane have prompted protests by Okinawa residents concerned about its use on the island.