Attempts to reduce civilian casualties caused by US-led forces in Afghanistan have led to a decline in insurgent attacks in some areas, a report says.
The document by America's National Bureau for Economic Research analysed incidents involving more than 4,000 civilian casualties in Afghanistan.
The curbs on aerial bombing and mortar fire were introduced last year by the recently sacked Gen Stanley McChrystal.
The general ended his army career at a ceremony in Washington on Friday.
Meanwhile, military officials confirmed on Saturday that four US personnel were killed in southern Afghanistan - continuing a recent upsurge in violence there.
Gen McChrystal was fired from his job as commander of multinational forces in Afghanistan by US President Barack Obama last month over a magazine interview in which he made disparaging remarks about the president and senior colleagues.
In an emotional farewell speech at Fort McNair parade ground, Gen McChrystal said his service had not ended as he had hoped, but he regretted few decisions he had made on the battlefield and was optimistic about his future.
Gen McChrystal, his wife Annie by his side, was given full military honours including a 17-gun salute.
US Defence Secretary Robert Gates paid tribute to him, saying: "Over the past decade, arguably no single American has inflicted more fear, more loss of freedom and more loss of life on our country's most vicious and violent enemies than Stan McChrystal."
Gen McChrystal's successor, Gen David Petraeus, is reportedly considering loosening the restrictions on international forces.
The authors of the report by the Massachusetts-based National Bureau of Economic Research say they analysed 15 months of data on military clashes and incidents totalling more than 4,000 civilian deaths in a number of Afghan regions in the period ending on 1 April.
They say that in areas where two civilians were killed or injured by Nato's International Security Assistance Force (Isaf), there were on average an extra six violent incidents between insurgents and US-led troops in the following six weeks.
The report concludes that civilian deaths frequently motivate villagers to join the ranks of insurgents.
"In Afghanistan, when Isaf units kill civilians, this increases the number of willing combatants, leading to an increase in insurgent attacks."
"Local exposure to violence from Isaf appears to be the primary driver of this effect."
The curbs were imposed by Gen McChrystal in an effort to win more Afghan hearts and minds.
Those rules ban air and mortar strikes on houses unless allied troops are in immediate danger.
But some soldiers have complained that the restrictions make their jobs more dangerous.