Amnesty said it had gathered evidence of "a deeply flawed US military justice system that cements a culture of impunity" in dealing with Afghan civilian deaths and injuries caused by US-led NATO coalition operations since 2001.

President Hamid Karzai has often castigated US forces for civilian casualties and he welcomed the release of the Amnesty report, though it triggered a firm response from the US and NATO's International Security Assistance Force (ISAF).

Amnesty researchers interviewed 125 Afghans who had first-hand information on 16 separate attacks that resulted in civilian casualties, as well as collating data from 97 reported incidents in the last seven years.

An Amnesty spokesman said its data that thousands of civilians had been killed by US forces was based on UN reports on civilian casualties, a Science magazine investigation in 2011 and other sources, but it gave no total death toll.

"The US military justice system almost always fails to hold its soldiers accountable for unlawful killings and other abuses," said Richard Bennett, a director of Amnesty International.

"None of the cases that we looked into -- involving more than 140 civilian deaths -- were prosecuted by the US military. Evidence of possible war crimes and unlawful killings has seemingly been ignored."

The Amnesty report, entitled "Left in the Dark", detailed a US bombing in 2012 when women were collecting firewood in the mountains of Laghman province.

Seven women and girls were killed and seven more were injured.

Ghulam Noor, who lost his 16-year-old daughter Bibi Halimi in the attack, brought the bodies to the district centre after hearing NATO forces claimed that only insurgents had been killed.

"We had to show them that it was women," Noor told Amnesty. "I have no power to ask the international forces why they did this. I can't bring them to court."

Amnesty said villagers filed complaints with the provincial governor, but international forces are immune from Afghan legal processes and no one ever contacted family members to investigate the attack.

NJF/NJF