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.

British media have 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.

British Defence minister Philip Hammond, speaking on BBC television, stressed that the rules of engagement must be followed.

"Everybody serving in theater knows the rules of engagement, they carry cards in their uniforms with the rules on them in case they need to remind themselves," he said.

"I can't comment on the specifics of this case. They are not out there, this is something that happened last year. These people were back in the UK and not in Afghanistan at the moment," he said. "We are very determined that rules of engagement will be followed, that any abuse will be dealt with through the normal processes of service justice and that is what is happening now."

Hammond also said Britain plans to withdraw thousands of troops from Afghanistan next year, as pressure mounts to end British involvement in the costly and unpopular war.

Some 500 troops are due to be repatriated by the end of this year, leaving around 9,000. Hammond said he expected thousands of those remaining to go home in 2013, but not the majority, indicating a maximum withdrawal of around 4,500 personnel.

All British combat personnel are due to be withdrawn by the end of 2014.

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.

AFP - Reuters