A U.S. service member reportedly walked out of a military base in southern Afghanistan on Sunday and went on a shooting spree in the middle of the night, opening fire on three nearby homes and killing at least 16 Afghan civilians. Afghan President Hamid Karzai said the dead included nine children and three women. Karzai called the killings an "assassination" that "cannot be forgiven." The U.S. soldier has been detained, but it’s not immediately known what prompted the shooting. Anti-American sentiments have been high since it was revealed last month that U.S. soldiers had accidentally burned a number of copies of the Muslim holy book the Quran, which sparked a wave of angry, deadly riots.