Afghan officials said Sunday that one or more U.S. soldiers shot dead 16 civilians -- including nine children -- in what witnesses called a massacre.
NATO said they had detained one U.S. soldier in the killings, and U.S. officials said the soldier was a staff sergeant.
The incident -- one of the worst of its kind since the U.S.-led invasion of Afghanistan in 2001 -- quickly inflamed severely strained relations between Washington and Kabul. Afghan President Hamid Karzai condemned the rampage as "intentional murders" and demanded an explanation from the U.S.
In an emailed statement to media, the Afghan Taliban said it would seek revenge for the killings.
The U.S. Embassy in Kabul warned that anti-American reprisals were possible following the deaths, which come weeks after U.S. soldiers triggered widespread outrage by burning copies of the Quran at a NATO base. At least 30 people died in protests against the burnings.
Neighbors and relatives of the dead said they had seen a group of U.S. soldiers arrive at their village in Kandahar's Panjwayi district at about 2 a.m. The soldiers entered homes and opened fire, they said.
A senior U.S. defense official in Washington rejected witness accounts that several apparently drunk soldiers were involved. "Based on the preliminary information we have, this account is flatly wrong," the official said. "We believe one U.S. service member acted alone, not a group of U.S. soldiers."