BELANDAI, Afghanistan (Reuters) - Bursts of gunfire shook Jan Agha out of bed in his village in Afghanistan's Kandahar province. His father peeped nervously through a window curtain at the lane outside.
Suddenly, more shots rang out. His father was hit in the throat and the face. He died instantly.
Afghan officials say Western forces shot dead 16 civilians including nine children in southern Kandahar province on Sunday in a rampage that witnesses said was carried out by American soldiers who were laughing and appeared drunk.
Only one U.S. soldier appeared to have been involved in the shootings, a U.S. official in Washington said, but that is not what witnesses were saying.
Agha, 20, said American soldiers who had opened fire in the early hours entered the family home and waited in silence for what seemed an eternity. He lay on the floor, pretending to be dead.
"The Americans stayed in our house for a while. I was very scared," he told Reuters.
"My mother was shot in her eye and her face. She was unrecognizable. My brother was shot in the head and chest and my sister was killed, too."
Agha's account of multiple American soldiers shooting villagers could not be immediately verified.
NATO's International Security Assistance Force (ISAF) said it had detained one of its soldiers and that an investigation was under way. It said the soldier reportedly went to more than one village near his base.
President Hamid Karzai's office, however, said in a statement he had spoken by telephone to a young boy who was wounded in the shootings who described how American soldiers had entered his house and opened fire on his family.
The attack, described by the Afghan defense ministry as a "horrific, inhumane act", was one of the worst such incidents since the U.S.-led invasion of Afghanistan in 2001.
It was not clear what mission the U.S. soldier or soldiers were involved in.
Reuters television footage of the aftermath of the shootings showed beefed up security in the village, which appeared to have Western forces positioned on its edges.
Civilian deaths are a major source of tension between Washington and Kabul.
The latest such killings could be especially damaging, coming just a few weeks after U.S. soldiers burned copies of the Koran, the Muslim holy book, outside a NATO base.
That incident, which NATO called a tragic blunder, triggered widespread violent protests. Afghan forces turned their weapons on American soldiers, killing six in several separate shootings.
The crisis in ties between Washington and Kabul will likely deepen once details of the rampage in Kandahar -- the Taliban heartland -- spread across a country that has grown increasingly incensed by what many Afghans see as heavy-handed U.S. tactics.
NATO's top commander in Afghanistan, Gen. John Allen, promised a speedy investigation.
Another witness, Agha Lala, who is in his 40s, said he was awoken by gunfire at about 2 a.m.
"I watched them from a wall for a while. Then they opened fire on me. The bullets hit the wall. They were laughing. They did not seem normal. It was like they were drunk," he said.
After rushing to his home and hiding all night, Lala, who is no relation to Jan Agha, went to check on the neighbors.
"It was a slaughter. The bullet-riddled bodies were all over the room and it seemed they were burned with curtains and blankets that were torched," he said.
"Is this what the Americans call an assistance force? They are beasts and have no humanity. The Taliban are much better than them."
Blood was splattered in one house in the village and there were bullet holes in the walls.
The Koran burnings and the shootings could hinder U.S.-led efforts to pacify Afghanistan before foreign combat troops leave at the end of 2014.
The United States had just made some progress in trying to reach a Strategic Partnership Agreement which would allow long-term American involvement in the country after 2014.
The two sides signed a deal on Friday on the transfer of a U.S.-run prison at Bagram airbase, where the Korans were burned, to Afghan authorities, something President Karzai had demanded.
Strategic considerations didn't figure in Haji Samad's emotions. Like other villagers, he now sees the Americans as the enemy.
Samad said he had been away when the violence hit Belandai but he realized something was wrong when he saw villagers gathered outside his home.
"I saw all 11 of my family members, including my children and grandchildren, who were killed," he said, crying. "They dropped some chemical materials on the bodies and burned them."
Writing by Michael Georgy, editing by Dean Yates and Michael Roddy