The Defense Ministry on Tuesday concluded that pilot error caused the fatal crash of an MV-22 Osprey in Morocco in April, an accident that set off a strong outcry against the deployment of the airplane-helicopter hybrid in Japan.

A 15-member expert panel launched by the ministry in July confirmed a U.S. Marine Corps report earlier this month that ruled out mechanical error and safety problems with the Osprey itself, marking a step forward in the planned deployment of the transport aircraft in Okinawa in October.

"The accident is largely attributable to the blatant breach of the manual by the copilot," said Tetsuro Kuroe, deputy director general of the ministry's Bureau of Defense Policy Bureau and head of the investigation panel.