Seven British Royal Marines have been arrested on suspicion of murder — an unusual case that could cause a backlash from Afghans and further erode efforts to provide political stability to Afghanistan.

The arrests relate to an incident in Afghanistan last year, and the Defense Ministry said it involved an insurgent rather than a civilian. It comes at a time when relations between NATO forces and the Afghan government are at a low ebb, as they attempt to quash the resilient Taliban insurgency after more than a dozen years of war.

Military experts said Friday the case is rare, as the Royal Marines are known for having a high level of training that would include instruction on acting with restraint.

Michael Clarke of the Royal United Services Institute says the spirit of the unit usually prevents misbehavior, and that having seven people involved in a single case will heighten the political embarrassment.

"This is a politically charged issue," he said. "It destroys so much work that has been done in the last months."

Though international officials are already starting to transfer full control of security to the Afghans, ethnic tensions still simmer and the government still does not have authority in all parts of the nation. Political leaders worry that the country could even fracture along ethnic lines once the foreign troops leave by the end of 2014, as it did after the Soviet exit from Afghanistan in February 1989.

The suggestion of murder is particularly unfortunate news at the moment — though no one has yet been charged. The incident is believed to be the first of this magnitude involving British Marines and an insurgent during the Afghan conflict, and the ministry said the arrests announced Thursday night underlined its commitment to making sure that British soldiers act in accordance with the rules of engagement.

Afghan Defense Ministry spokesman Gen. Zahir Azimi said the Afghan government welcomed the arrests because it means that the law is being implemented.

The incident took place in Helmand province, which was the centerpiece of the U.S. surge that sent tens of thousands of U.S. Marines to join British Royal Marines there in 2010. They fought pitched battles against entrenched Taliban insurgents in the central Helmand River Valley before the pace of combat eased in 2011.

The brigade believed to be involved in the incident, 3 Commando, was in the thick of the fighting — which would have heightened tensions already soaring amid heat, fear and other strains of combat. The rules of engagement in general would allow them to fire on someone that is a threat or someone involved in a hostile act, like planting a bomb, Clarke said.

Eric Grove, director of Center for International Security and War Studies at the University of Salford, said the rules of engagement would spell out at what point the enemy is no longer a threat and when the Geneva Conventions on the treatment of prisoners takes effect.

"They are very much an elite force," he said of the British Marines. "They would normally be very good at showing restraint in action."

He said that the arrested Marines have "very much let the side down."

Past incidents involving abuses by coalition soldiers have sparked protests and riots in Afghanistan, damaging relations with the government of Hamid Karzai. Also eroding the relations have been a rising tide of attacks in which Afghan soldiers or police assault their international allies — endangering the partnership that is critical to training Afghan security forces and withdrawing international troops.

But while there have been some allegations of abuse against civilians, the case revealed Thursday is unusual in that it involves an insurgent.

However, allegations of British misconduct in general have been rare in Afghanistan, with some of the experts noting that Britain had learned its lessons from several appalling incidents in Iraq.

Britain's six-year military presence in southern Iraq spawned multiple allegations of torture and abuse. The most notorious case involved a hotel receptionist, Baha Mousa, who died while in custody at a British base after being detained in a raid in Basra in September 2003. Britain's defense authorities later apologized for the mistreatment of Mousa and nine other Iraqis and paid a $4.8 million (3 million pound) settlement. Six soldiers were cleared of wrongdoing at a court martial, while another pleaded guilty and served a year in jail.

The government says abuse was committed by only a few soldiers, but lawyers for the alleged victims say it was systemic.

The Defense Ministry's terse statement Thursday suggested that the military was moving to control the incident, and trying to make certain the potentially lurid details were kept under wraps. The statement said the seven were arrested Thursday by Royal Military Police, but did not name the Marines.

While the ministry said the Marines were not arrested in Afghanistan, it would not specify where the arrests took place or give any further details on the alleged murder.

"The investigation will now be taken forward and dealt with by the Service Justice system," the ministry said in a statement, adding that "as with any serious incident of this nature, there will be an internal review to identify lessons learned."

Britain has 9,500 troops in Afghanistan — the second largest foreign force after the United States — based in the southern Helmand province.

About 500 troops will leave this year, ahead of the withdrawal of all international forces at the end of 2014.


Associated Press Writers Deb Riechmann in Kabul and Mirwais Khan in Kandahar, Afghanistan, contributed to this report.