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

It is believed to be the first time that British servicemen have faced such charges during the conflict.

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

Two more marines were arrested, one Friday and one 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, without saying when they were charged.

"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 British police found suspicious footage on a serviceman's laptop.

The MoD said the incident, which it did not describe in detail, followed an "engagement with an insurgent" and that no civilians were involved.

It occurred at a time when Royal Marine 3 Commando Brigade was based in the southern Helmand province.

Defence Minister Philip Hammond stressed that the rules of engagement must be followed on the battlefield.

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

"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.

"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."

In Kabul, the Afghan defence ministry hailed the charges.

"We do welcome the move by Britain to bring to justice those who break the laws of war," spokesman General Zahir Azimi told AFP. "We hope this process continues."

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.

Hammond on Sunday said it was now possible "to have a significant reduction" in British force numbers in Afghanistan by the end of next year.

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