NATO will investigate whether a grenade thrown by American military forces killed a British aid worker during a rescue attempt in Afghanistan last week, an alliance spokesman said Monday.

Linda Norgrove, 36, was killed Friday in the raid by U.S. forces in Afghanistan's eastern Kunar province, after she and three colleagues were kidnapped two weeks earlier. NATO initially said Norgrove died when captors detonated a bomb as NATO forces attempted to free her.