Eight American service members were killed last week when tilt-rotor aircraft crashed during training mission

The United States said on Wednesday it was grounding its military fleet of V-22 Osprey aircraft after a fatal crash last week off the coast of Japan that killed eight people onboard.

“Preliminary investigation information indicates a potential material failure caused the mishap, but the underlying cause of the failure is unknown at this time,” US Air Force Special Operations Command (AFSOC) said in a statement.