An American commander in Afghanistan has said that he is "deeply ashamed" by the killings of 19 Afghan civilians by US Marines in early March.
Coalition forces say they must reduce civilian deaths
He said that the military had paid condolence payments to the families in the eastern province of Nangarhar.
Western forces have been accused of carelessness over civilian lives when attacking the Taleban and their allies.
It has become a major issue, with Nato recently saying that its biggest error last year was killing civilians.
In January, it promised to do better.
"I stand before you today, deeply, deeply ashamed and terribly sorry that Americans have killed and wounded innocent Afghan people," US army spokesman Col John Nicholson told reporters in Washington by video conference from Afghanistan.
"The deaths and wounding of innocent Afghans at the hands of Americans is a stain on our honour and on the memory of the many Americans who have died defending Afghanistan and the Afghan people.
"We made official apologies on the part of the US government and payments of about $2,000 for each death," he said, after US officials visited some of the families left bereaved by the incident.
US forces were accused of killing the civilians during shooting near the city of Jalalabad.
Journalists said at the time that US troops confiscated their photos and video footage of the aftermath of the violence.
The Americans said the fighting started when a convoy of Marines was attacked by a suicide bomber and came under co-ordinated small-arms fire.
Local accused US soldiers of targeting civilians in Nangarhar
They said that their soldiers returned fire, and acknowledged that at least eight Afghan civilians had been killed, with a further 35 injured.
Reports said that as they left the scene along a busy highway, the Americans fired indiscriminately on civilians and their vehicles.
Afghan President Hamid Karzai strongly condemned the incident at the time.
Thousands of local people took to the streets shortly after the attack to protest against what happened.
The Associated Press news agency said it would complain to the US military after journalists said US soldiers allegedly deleted footage of the aftermath of the Nangarhar violence.
Freelance journalists working for the Associated Press said troops erased photos and video showing a vehicle in which three people were shot dead during the incident.
US-led forces say they kill fewer civilians than the Taleban
A US military commander determined that the Marines used excessive force and referred the case for possible criminal investigation.
Correspondents say that military killings of civilians have eroded Afghan support for international forces and have put the Western-backed government in Kabul under pressure.
On Thursday, Nato forces vowed to improve co-ordination with the Afghan authorities to avoid civilian deaths.
Their pledge follows the reported deaths of about 50 civilians last week in fighting in western Afghanistan between US-led troops and militants.
In recent days there have been protests by Afghans in different parts of the country - including Jalalabad - over civilian killings.
The bloodshed has returned to levels not seen since the fall of the Taleban in 2001, and a quarter of more than 4,000 people killed last year were believed to have been civilians.
Correspondents say fewer civilians are killed by international forces than in suicide and other attacks by the Taleban.