Afghan and US officials differ over how many civilians died
A US military inquiry has uncovered serious mistakes made when US forces bombed suspected Taliban positions in Afghanistan in May, US officials say.
Dozens of civilians were killed in the air strikes in western Farah province.
Some of the raids would have been called off, had the rules of engagement been followed strictly, unnamed officials were quoted as saying.
Meanwhile, the general named as the next US commander in Afghanistan has said civilian deaths must be reduced.
Gen Stanley McChrystal said civilian casualties caused by US and Nato-led forces could alienate the Afghan people.
Civilian casualties are causing growing public outrage in Afghanistan and friction between the US and Afghan governments.
The publication of the US military report is expected later this week.
But some of the details have been leaked and the BBC's Jonathan Beale in Washington says this is the closest the Pentagon has come to admitting that mistakes were made when US military planes carried out attacks last month.
The Afghan government says 140 people were killed in the strikes in early May, while the Americans say 20-30 people died.
"American personnel made significant errors in carrying out some of the air strikes in western Afghanistan on May 4 that killed dozens of Afghan civilians," a New York Times report said, citing an unnamed senior US military official.
"In several instances where there was a legitimate threat, the choice of how to deal with that threat did not comply with the standing rules of engagement," the official was quoted as saying.
"Errors were made," in the attack, the Associated Press also quoted an official as saying.
In one case, a compound of buildings where suspected militants were massing was struck, even though it was in a densely populated area and there was no imminent threat, the New York Times said.
"Had the rules been followed, at least some of the strikes by American warplanes against half a dozen targets over a seven-hour period would have been aborted," the article said.
Change in strategy
Gen McChrystal, currently the director of US Joint Chiefs of Staff, was named last month to replace Gen David McKiernan and is currently undergoing confirmation hearings in the US Senate.
Gen McChrystal: 'Critical point'
His appointment comes as the US boosts troop numbers in Afghanistan and prepares for a change in strategy.
Gen McKiernan's time as US commander in Afghanistan has coincided with a surge in violence.
US Defence Secretary Robert Gates said his replacement would bring "fresh thinking, fresh eyes" to the problem.
On Tuesday, Gen McChrystal told senators: "If defeating an insurgent formation produces popular resentment, the victory is hollow and unsustainable."
He added: "This is a critical point. It may be the critical point. This is a struggle for the support of the Afghan people.
"Our willingness to operate in ways that minimise casualties or damage - even when doing so makes our task more difficult - is essential to our credibility," he said.
"With the appropriate resources, time, sacrifice and patience, we can prevail."
Gen McChrystal warned that Afghanistan would descend back into civil war and al-Qaeda would use the country as a base if the United States and its allies failed in their mission.