Five of Britain's elite Royal Marines have been charged with murder following an engagement with an insurgent in 2011, the Ministry of Defence said on Sunday.

British military police had arrested seven Royal Marines last Thursday on suspicion of murder in connection with the incident.

Two more marines were arrested, one on Friday and one on Saturday, taking the total number of arrests to nine, an MoD spokesman said. Four have since been released without charge.

"The Royal Military Police (RMP) has referred the case of the remaining five Royal Marines to the independent Service Prosecuting Authority (SPA)," the spokesman added.

"Following direction from the SPA these marines have now been charged with murder and they remain in custody pending court proceedings.

"It would be inappropriate to comment further on this ongoing investigation," he added.

The BBC meanwhile reported that the marines were arrested after suspicious footage was found on a serviceman's laptop by British police.

The arrests are thought to be the first time that British servicemen have been held on suspicion of such charges during the Afghanistan conflict.

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.