Even as the British army was still reeling from allegations of misconduct by its troops in Iraq, seven Royal Marines, who served in Afghanistan, were arrested on suspicion of the murder of a Taliban militant.

The Ministry of Defence said the arrests related to an incident that followed an “engagement with an insurgent” in Helmand last year. It said no civilians were involved.

Elite unit

All those arrested belonged to the elite 3 Commando Brigade, rated highly for its record in Afghanistan until now. According to media reports, the incident came to light accidentally after the Royal Military Police, investigating a case involving pornographic material, found footage on a laptop showing a group of soldiers huddled around an injured man lying on the ground. The man later died.

The MoD declined to give details saying it would be “inappropriate to make any further comment while the investigation is under way”.

“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 U.K. personnel act in accordance with their rules of engagement and our standards,” a spokesman said.

The Afghan Defence Ministry said the incident highlighted the need for NATO forces to respect the laws of war.