Military documents laid bare in the biggest leak of secret information in US history suggest that far more Iraqis died than previously acknowledged during the years of sectarian bloodletting and criminal violence unleashed by the 2003 US-led invasion.
The accounts of civilian deaths among nearly 400,000 purported Iraq war logs released Friday by the WikiLeaks website include deaths unknown or unreported before now - as many as 15,000 by the count of one independent research group.
The field reports from US forces and intelligence officers also indicate US forces often failed to follow up on credible evidence that Iraqi forces mistreated, tortured and killed their captives as they battled a violent insurgency.
The war logs were made public in defiance of Pentagon insistence that the action puts the lives of US troops and their military partners at risk.
Although the documents appear to be authentic, their origin could not be independently confirmed, and WikiLeaks declined to offer any details about them.
The 391,831 documents date from the start of 2004 to January 1, 2010, providing a ground-level view of the war written mostly by low-ranking officers in the field.
The dry reports, full of military jargon and acronyms, were meant to catalogue "significant actions" over six years of heavy US and allied military presence in Iraq.
The Pentagon has previously declined to confirm the authenticity of WikiLeaks-released records, but it has employed more than 100 US analysts to review what was previously released and has never indicated that any past WikiLeaks releases were inaccurate.
Casualty figures in the US-led war in Iraq have been hotly disputed because of the high political stakes in a conflict opposed by many countries and a large portion of the American public.
Critics on each side of the divide accuse the other of manipulating the death toll to sway opinion.
Iraq Body Count, a private British-based group that has tracked the number of Iraqi civilians killed since the war began, said it had analysed the information and found 15,000 previously unreported deaths, which would raise its total from as many as 107,369 civilians to more than 122,000 civilians.
It said most of the newly disclosed deaths included targeted assassinations, drive-by shootings, torture, executions and checkpoint killings.
Al-Jazeera, one of several news organisations provided advance access to the WikiLeaks trove, reported the documents show 285,000 recorded casualties, including at least 109,000 deaths. Of those who died, 66,000 were civilians, nearly two-thirds of the total.
The Iraqi government has issued a tally claiming at least 85,694 deaths of civilians and security officials were killed between January 2004 and October 31, 2008.
In July of this year, the US military quietly released its most detailed tally to date of the deaths of Iraqi civilians and security forces in the bloodiest years of the war.
That US body count, reported this month, tallied deaths of almost 77,000 Iraqis between January 2004 and August 2008 - the darkest chapter of Iraq's sectarian warfare and the US troop surge to quell it.
The new data was posted on the US Central Command website without explanation.
In August 2008, the Congressional Research Service said the US military was withholding statistics on Iraqi civilian deaths.
The Pentagon did publish in June 2008 a chart on civilian death trends by month that showed it peaking at between 3,500 and 4,000 in December 2006. But it did not release the data used to create the chart.
In 2006 and 2007, the Bush administration and military commanders often played down the extent of civilian killings from revenge killings, blood feuds and mob-style violence in Iraq, much of which had no direct effect on US forces.
Administration figures repeatedly denied Iraq was sliding into civil war. The war did not begin to turn around in a lasting way until the 2007 "surge" of US troops and the decision of key Sunni leaders to cut ties with al-Qaida.