Kabul Afghans have expressed doubt that a single US Army soldier could have shot and killed 16 civilians in houses over two kilometres apart and burned the bodies afterward.
The killings in southern Afghanistan have reignited fury at the US presence following a wave of deadly protests over Americans burning Qurans.
The US military has said there is no indication that more than one soldier carried out the attacks in two villages in Kandahar province before dawn on Sunday.
The soldier blamed for the shootings is in custody. But villagers told Afghan officials they heard shots being fired from several directions.
The attack threatens to bring the widest breach yet in US-Afghan relations, raising questions both in Washington and Kabul about why American troops are still fighting in Afghanistan after ten years of conflict and the killing of Osama Bin Laden.
US and Afghan officials have said that the attack began around 3am in the villages of Balandi and Alkozai in Panjwai district, a rural region outside Kandahar that is the cradle of the Taliban and where coalition forces have fought for control for years.
The villages are roughly 500 metres from a US base. Villagers told The Associated Press on Sunday that a single soldier roamed from house to house firing on those inside.
They said he entered three homes in all and set fire to some of the bodies. Eleven of the dead were from a single family, and nine of the victims were children. But Abdul Rahim Ayoub, a lawmaker from Kandahar province, said the houses that were attacked were over two kilometres apart, raising questions about how a single soldier could have carried out all of the shootings.
"It is not possible for only one American soldier to come out of his base, kill a number of people far away, burn the bodies, go to another house and kill civilians there, then walk at least 2km and enter another house, kill civilians and burn them," said Ayoub.
Abdul Gani, a local councillor in Panjwai district, said local villagers reported seeing two groups of soldiers.
"The villagers said they were hearing machine gun fire and pistol fire from different directions," said Gani.
A spokesman for US-led forces, US Army Lieutenant-Colonel Jimmie Cummings, said yesterday that their reports still indicate a single soldier carried out the attacks.
"There's no indication that there was more than one shooter," said Cummings.
The Afghan defence ministry said its initial reports also indicate one soldier carried out the attacks, but they left open the possibility there could have been be more.
"The Afghan defence ministry requests a trial for the perpetrator or perpetrators of this attack," said a statement.
Afghan President Hamid Karzai also left open the possibility of more than one shooter in a statement Sunday. He initially spoke of a single US gunman, then referred to "American forces" entering houses. The statement quoted a 15-year-old survivor named Rafiullah, who was shot in the leg, as telling Karzai in a phone call that "soldiers" broke into his house, woke up his family and began shooting them.
"This is an assassination, an intentional killing of innocent civilians and cannot be forgiven," Karzai said.
US officials have identified the shooter as an Army staff sergeant and said initial reports indicated he returned to the base after the shooting and turned himself in.
The suspect, from Joint Base Lewis-McChord, Washington, was assigned to support a special operations unit of either Green Berets or Navy Seals engaged in a village stability operation, said a US official.