The US soldier walked off his base, heavily armed and with night vision equipment, and broke into three village homes before dawn Sunday, killing 16 people including women and children, according to Western and Afghan sources.
Some bodies bore blackened burn marks, according to an AFP correspondent who saw them at the villages in the southern province of Kandahar.
It is the latest in a series of actions by American troops that has provoked outrage in Afghanistan, and comes weeks after the burning of Korans at a US base provoked riots that killed 40 people and plunged ties to an all-time low.
The Taliban, leading a 10-year insurgency against US-led foreign troops and the government in Kabul, threatened to take revenge against "sick-minded American savages ... for every single martyr".
The statement on their website came after the US embassy urged its citizens to take extra precautions, warning against "a risk of anti-American feelings and protests in coming days especially in eastern and southern provinces".
A soldier has been detained and the United States has offered condolences to the families and pledged that action will be taken against anyone found guilty.
President Barack Obama telephoned Afghan President Hamid Karzai to promise a speedy investigation into the "shocking" killings, which fanned already smouldering anger among Afghans over the burning of the Korans.
Sunday's massacre poses an acute test of the US-Afghan alliance, as the two countries pursue difficult talks on securing a strategic pact to govern their partnership once foreign combat troops leave Afghanistan in 2014.
The proposed strategic pact would likely cover the legal status of any US troops remaining in Afghanistan to help Kabul with intelligence, air power and logistics in the fight against Taliban insurgents.
In Iraq, Washington abandoned its pursuit of a strategic partnership deal and pulled out all its combat troops, leaving no residual force, after failing to get Baghdad to grant its soldiers legal immunity.
A survey by ABC News and The Washington Post says that 60 percent of Americans now believe the Afghan war is not worth its costs and that 54 percent want to pull out US troops even if the Afghan army is not adequately trained.
Karzai reacted with anger to what he called the deliberate and unforgivable killings in Kandahar, the province where the Taliban were created.
"When Afghan people are killed deliberately by US forces, this action is murder and terror and an unforgivable action," he said.
He spoke by telephone with the families of those killed, including Rafihullah, a 15-year-old boy wounded in the leg who told the president the soldier had torn the dresses of the women in the house and insulted them.
"He came to my uncle's home, he was running after women, he was tearing their dresses, insulting them," Rafihullah said on an audiotape of the conversation heard by AFP.
"He killed my uncle and killed our servant and killed my grandma, he shot dead my uncle's son, his daughter," the boy said.
The Taliban wasted no time in trying to capitalise on the killings, sending fighters to mosques in Kandahar's Panjwayi district as the funerals of the victims of the shootings took place, urging villagers to rise up.
"They were telling the people: 'The invading infidel Americans come to your homes, insult your women and kill your children, what are you waiting for? You should come out and demonstrate'," local resident Abdul Khaliq told AFP.
Kandahar is a stronghold of the Taliban fighting to oust Karzai's government, which is supported by some 130,000 US-led NATO troops.
"A large number from amongst the victims are innocent children, women and the elderly, martyred by the American barbarians who mercilessly robbed them of their precious lives," the Taliban said.
In November, the ringleader of a rogue American military "kill team" charged with murder for shooting civilians for sport was found guilty and sentenced to life in prison by a military panel.
But observers say the vast majority of civilian deaths in the Afghan war are caused by the Taliban. A total of 3,021 civilians died in the war last year, according to a UN report, which blamed 77 percent of the deaths on the militia.
COMMENTS (14)
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Yes Taliban must have to do so at any cost.
US is going to be punished soon
@Ali S: Nice to note that you got the intended sarcasm in my remark.
@Parvez:
Yeah they can see how well Pakistan is doing under "democracy"
Have you noted the thing auditor using koran instaed of proper wording with respect "Quran".
Only the Afghan soldiers and Police who are mentored by these 'barbarians' could teach them a lesson. Like they did after the Quran burning.
Talibans are not Red Indians fighting with arrows only... They are native and still in large numbers. World kept silence on this crime while they rise up for Syria and Libya. Hippocratic attitude of Human Rights Champions is obvious. They minus Muslims from the definition of human so how can you expect them to stand against such brutality. Still they rant that Taliban killed more than them.. are you competing with civilian killings??? Shame on us who give logistic support to them and are equally responsible for bringing US here in this region.
Who else here has a good idea what 15 year old Rafihullah's career plans are?
Someone should advise the Taliban that democracy is the best revenge.
Hopefully it will not be innocent Pakistanis.
When we will realize who real terrorists are.
yeah teach a lesson to invaders
Insha'Allah They will revenge.
US soldier’s killing spree of 16 villagers in Afghanistan
Look who's the barbarian!