A US soldier in Afghanistan has gone on the rampage, killing at least 16 civilians, according to reports.
The incident happened in the village of Belandi in the Panjway district of Kandahar province, in the south of the country. The soldier is reported to have been detained.
Nine children are thought to be among the dead - reportedly all shot inside a single house.
"It was a shooting incident involving multiple civilians wounded," US military spokesman, Captain Justin Brockhoff, told Reuters.
NATO said it was a "deeply regrettable incident", which it was investigating.
"We extend our thoughts and concerns to the families involved," said a NATO spokesperson.
The region where the atrocity took place is a former Taliban stronghold, but was captured by US forces during the surge in troops in the country ordered by Barack Obama in 2009.
The apparent massacre is certain to raise tensions in the region further, after mass protests followed the burning of the Koran by two American soldiers at the end of last month. Some analysts viewed the book-burning as a "tipping point" for the country, likely to substantially increase support for the Taliban.
The deteriorating security situation led to the British embassy removing all non-essential staff from its offices in the Afghan capital, Kabul.
Sky News quotes the US embassy in Kabul as saying: "We deplore any attack by a member of the US armed forces against innocent civilians, and denounce all violence against civilians.
"We assure the people of Afghanistan that the individual or individuals responsible for this act will be identified and brought to justice."