The Afghan authorities have launched an investigation into the circumstances of a militant attack on a US marines' convoy in which eight civilians died.
Thirty-five people were also injured during the incident
The incident, in which 35 people were also injured, occurred on a road from the city of Jalalabad to Pakistan.
A suicide bomber reportedly targeted the convoy, sparking a fire fight.
Thousands of local people took to the streets on Sunday to protest against the incident, accusing the Americans of deliberately firing on the civilians.
The US military described the attack, 50 km (31 miles) from the eastern city of Jalalabad, as a "complex ambush".
It said the convoy of marines was attacked by a suicide bomber driving a minibus packed with explosives and also came under co-ordinated small-arms fire from several directions.
Their soldiers returned fire, the military said, and at least eight Afghan civilians were killed, with a further 35 injured.
US military spokesman Maj William Mitchell said: "We certainly believe it's possible that the incoming fire from the ambush was wholly or partly responsible for the civilian casualties."
However, Mohammad Khan Katawazi, chief of Shinwar district, said the US troops treated everyone as a potential attacker.
One injured civilian, Tur Gul, told the Associated Press news agency: "They opened fire on everybody, the ones inside the vehicles and the ones on foot."
"When we parked our vehicle, when they passed us, they opened fire on our vehicle," said Mohammad Ishaq, 15, who was also hit by bullets.
The BBC's Alastair Leithead in Kabul says there has been a huge increase in the number of suicide attacks over the past 12 months, but a co-ordinated ambush is relatively rare.
The Afghan President, Hamid Karzai has repeatedly called on Western forces not to harm civilians.
Thousands of people gathered to demonstrate against the shooting, shouting "Death to America, Death to Karzai", and blaming the US patrol for shooting passers-by.
Our correspondent says there have also been other demonstrations in the same province, Nangarhar, recently, mainly at opium poppy eradication by government officials.
Local people accused the US soldiers of targeting civilians
Separately, two British servicemen were killed in the Sangin area of southern Helmand province on Saturday.
Twenty foreign soldiers have been killed in Afghanistan so far this year.
Nato fears that Taleban violence will escalate in several areas of Afghanistan as the winter snows thaw.
Nato commanders have said they need more soldiers to tackle the expected spring offensive.