KABUL, Afghanistan – Western military officials on Wednesday acknowledged a case of mistaken identity in the killings of four Afghan civilians in eastern Afghanistan — the second such lethal episode in just over a week.

NATO had initially described two of the four occupants of a car that was fired on Monday night by troops in Khowst province as “known insurgents.” The soldiers, whose nationality was not disclosed, unleashed a fusillade of bullets after the vehicle accelerated toward a military convoy, according to alliance officials’ account.

Family members and local officials had insisted that the group, which included three teen-age boys, was returning home from a sporting event.

They said none of the car’s occupants had links to the insurgency — in fact, one was a police officer. And they expressed vehement disbelief that the four, none of whom was armed, had demonstrated any hostile intent toward the Western troops.

The episode came seven days after American troops in Kandahar province — apparently believing themselves under imminent threat of attack — also fired on a vehicle approaching a military convoy. It turned out to be a passenger bus, and four Afghans aboard were killed, including a woman.

President Hamid Karzai condemned the killings even before NATO acknowledged its mistake. The incident is likely to add to a growing furor over civilian casualties, which have steadily increased as the nearly nine-year conflict has dragged on.