Seven Royal Marines have been arrested on suspicion of murder in an incident in Afghanistan in 2011, the BBC reported citing the British Ministry of Defense.

It is believed to be the first time UK servicemen have been detained on such charges during the conflict.

"The investigation will now be taken forward and dealt with by the service justice system. 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,” a ministry spokesman said as quoted by the BBC.

“It would be inappropriate to make any further comment while the investigation is under way,” he said.

The Ministry of Defense said the incident occurred after an "engagement with an insurgent," adding that no civilians were involved.

The engagement rules stipulate circumstances under which British forces were allowed to open fire, either when directly contacting the enemy or in order to prevent an imminent attack.

Over 20 servicemen from 3 Commando Brigade, based in Helmand in 2011, lost their lives last year during a summer tour of duty. Many more were injured.