A second cluster of similar shootings, all involving Royal Marine commandos in Helmand province, took place in a six-month period at the end of 2008, according to the log entries. Asked by the Guardian about these allegations, the Ministry of Defence said: "We have been unable to corroborate these claims in the short time available and it would be inappropriate to speculate on specific cases without further verification of the alleged actions."

Rachel Reid, who investigates civilian casualty incidents in Afghanistan for Human Rights Watch, said: "These files bring to light what's been a consistent trend by US and Nato forces: the concealment of civilian casualties. Despite numerous tactical directives ordering transparent investigations when civilians are killed, there have been incidents I've investigated in recent months where this is still not happening.

Accountability is not just something you do when you are caught. It should be part of the way the US and Nato do business in Afghanistan every time they kill or harm civilians." The reports, many of which the Guardian is publishing in full online, present an unvarnished and often compelling account of the reality of modern war.

Most of the material, though classified "secret" at the time, is no longer militarily sensitive. A small amount of information has been withheld from publication because it might endanger local informants or give away genuine military secrets. Wikileaks, whose founder, Julian Assange, obtained the material in circumstances he will not discuss, said it would redact harmful material before posting the bulk of the data on its "uncensorable" servers.

Wikileaks published in April this year a previously suppressed classified video of US Apache helicopters killing two Reuters cameramen on the streets of Baghdad, which gained international attention. A 22-year-old intelligence analyst, Bradley Manning, was arrested in Iraq and charged with leaking the video, but not with leaking the latest material. The Pentagon's criminal investigations department continues to try to trace the leaks and recently unsuccessfully asked Assange, he says, to meet them outside the US to help them. Assange allowed the Guardian to examine the logs at our request. No fee was involved and Wikileaks was not involved in the preparation of the Guardian's articles.