British military police on Thursday arrested seven members of the elite Royal Marines on suspicion of murder in Afghanistan in 2011, the Ministry of Defence (MoD) announced.

"The incident followed an engagement with an insurgent -- there were no civilians involved," said an MoD spokesman.

The investigation will now be conducted by the Service Justice system, which handles offences committed by British service personnel overseas, added the spokesman.

"These arrests demonstrate the department and the Armed Forces' determination to ensure UK personnel act in accordance with their Rules of Engagement and our standards," said the MoD statement.

The department said it would not be releasing any more information about the arrests, but vowed to conduct an internal review "to identify lessons learned.

"The nature of that review will reflect the developments in and, in due course, the outcome of the investigation," it added.

The Royal Marines, or "green berets", were formed in 1755 as marine infantry for the Royal Navy and have a reputation as some of the toughest military professionals in the world.

Britain still has some 9,500 troops in Afghanistan, all of whom are due to leave by the end of 2014.

Some 433 British personnel have been killed in the country since the start of the operation against the Taliban in 2001.

Prosecutors in April decided not to charge a British soldier with the murder of an Afghan man who had been digging near a military base in Helmand.

Duane Knott, a member of the Territorial Army volunteer reserve force, was investigated after shooting the man who he mistakenly believed was laying booby-trap explosives.

The Service Prosecuting Authority, set up to conduct independent prosecutions of military personnel, concluded there was no "realistic prospect of a conviction in this case."