McChrystal had apologised to Hamid Karzai, the Afghan president, shortly after the
"Inadvertently killing or injuring civilians is heartbreaking and undermines their trust and confidence in our mission. We will do all we can to regain that trust.''
The release of the report is part of a US effort to counter rising public anger in Afghanistan over civilian casualties.
The deadly attack occurred on February 21 after the unmanned Predator drone, controlled by a crew at Creech Air Force Base, Nevada, spotted three vehicles on a main road in Uruzgan province about 12km from where US Special Forces and Afghan soldiers were tracking suspected fighters, the report said.
Suspecting the convoy contained fighters, the ground commander ordered an
airstrike, and US helicopters fired missiles at the vehicles, it added.
But the attack order was based on inaccurate information from the Predator
crew and a flawed analysis of the situation by US commanders, according to Army Major General Timothy McHale, the author of the report.
|Nato forces have vowed to minimise civilian casualties during operations [AFP]
Poorly functioning command posts "failed to provide the ground force commander with the evidence and analysis that the vehicles were not a hostile threat and the inaccurate and unprofessional reporting of the Predator crewdeprived the ground force commander of vital information,'' McHale wrote.
"Information that the convoy was anything other than an attacking force was ignored or downplayed by the Predator crew,'' it said.
McHale also criticised commanders for failing to report "ample evidence'' of civilian casualties for nearly 12 hours after the attack, while they tried for confirmation.
The accidental killing of civilians by Nato forces has become a major source of friction between the Afghan government and its international allies, even though the United Nations says the overwhelming majority of civilian deaths are caused by the Taliban.
The issue has taken on new urgency as Nato prepares for a major operation to secure Kandahar, the largest city in the south of Afghanistan and a key Taliban stronghold.
Nato commanders believe securing the city is key to defeating the Taliban in the area.
The UN says at least 2,412 civilians were killed in the Afghan conflict in 2009 - a 14 per cent increase over the previous year.
Nato and Afghan government forces were responsible for 25 per cent of the deaths and of those, about 60 per cent were due to airstrikes, the UN said in a report published in January.