WASHINGTON – Each time U.S. or NATO forces accidentally kill Afghan civilians, insurgents and their sympathizers typically retaliate with six additional assaults on foreign forces over the next six weeks, researchers using newly declassified NATO data conclude.

A new study published by the National Bureau of Economic Research supports the prevailing view of counterinsurgency strategists who believe civilian casualties help Taliban recruiting drives. The study found that attacks on foreign forces increase slightly even when the insurgents are to blame for the deaths of noncombatants.

“Our results show that if counterinsurgent forces in Afghanistan wish to minimize insurgent recruitment, they must minimize harm to civilians despite the greater risk this entails,” says the study, to be released today through the Washington-based New America Foundation.

The principle that protecting civilians is the key to sidelining and ultimately defeating an insurgency is the heart of the strategy outlined by Gen. David Petraeus in Iraq and adapted for Afghanistan.

As applied by the former U.S. commander in Afghanistan, Gen. Stanley McChrystal, the strategy includes strict limits on U.S. air strikes and firepower.

Petraeus, who took over from McChrystal last month, is tweaking those rules but has said he will not lift them outright.

Petraeus told Congress last month that he remains convinced that heavy-handed tactics do more long-term harm than good.

He published a new manifesto on counterinsurgency Sunday that drives home that point.

“The people are the center of gravity,” Petraeus wrote in a memo to his troops.

“Only by providing them security and earning their trust and confidence can the Afghan government and ISAF prevail.”