The British Ministry of Defence says seven Royal Marines have been arrested on suspicion of murder.
The detentions relate to an incident in Afghanistan in 2011.
Military police say it follows an engagement with an insurgent and no civilians were involved.
The investigation will be conducted by the Service Justice system, the body which handles offences committed by British service personnel overseas.
Authorities declined to say anymore about the case.
The independent Service Prosecuting Authority says there is little chance of a conviction in this case.