Leaked Pentagon files obtained by the Guardian contain details of more than 100,000 people killed in Iraq following the US-led invasion, including more than 15,000 deaths that were previously unrecorded.

British ministers have repeatedly refused to concede the existence of any official statistics on Iraqi deaths. US General Tommy Franks claimed in 2002: "We don't do body counts."

The mass of leaked documents provides the first detailed tally by the US military of Iraqi fatalities. Troops on the ground filed secret field reports over six years of the occupation, purporting to tot up every casualty, military and civilian.

Iraq Body Count, a London-based group that monitors civilian casualties, told the Guardian: "These logs contain a huge amount of entirely new information regarding casualties. Our analysis so far indicates that they will add 15,000 or more previously unrecorded deaths to the current IBC total. This data should never have been withheld from the public."

The logs record a total of 109,032 violent deaths between 2004 and 2009. It is claimed that 66,081 of these were civilians. A further 23,984 deaths are classed as "enemy" and 15,196 as members of the Iraqi security forces. The logs also include the deaths of 3,771 US and allied soldiers.

No fewer than 31,780 of the total deaths are attributed to the improvised landmines laid around Iraq by insurgents. There were 65,439 successful "improvised explosive device" (IED) blasts in the period, according to the logs, with another 44,620 IEDs found in time and disarmed.

The other major recorded cause of death is the civil war that broke out during the US military occupation. There are 34,814 victims of sectarian killings recorded as murders in the logs. The worst single month was December 2006 when 2,566 Iraqis were found dead.

The data cannot be relied upon as a complete record of Iraqi deaths. IBC, for example, had previously calculated that up to 91,469 civilians were killed from various causes during the period covered by the leaked database. While detailing the 15,000 previously unknown deaths, it also omits many otherwise well-attested civilian fatalities caused by US troops themselves. Nor does the Pentagon data cover any of the initial invasion fighting throughout 2003; IBC has identified 12,080 purely civilian deaths in that year.

The US figure is far lower than another widely quoted estimate of more than 650,000 "excess deaths" extrapolated on a different basis and published in a 2006 study in the Lancet.

A key example of the failure by US forces to record civilian casualties they have inflicted comes in the two major urban battles against insurgents fought in 2004 in Falluja. Numerous buildings were reduced to rubble by air strikes, tank shells and howitzers, and there were well-attested deaths of hundreds of civilians. IBC has identified between 1,226 and 1,362 such deaths during April and November. But the leaked US internal field reports record no civilian casualties at all.

One of the most publicised allegations was that a clinic in central Falluja was shelled on 9 November. Doctors claimed to international media that two strikes on the roof had killed scores of patients and staff. The IBC puts the total number of civilian deaths at 59.

The US military maintained these claims were "unsubstantiated", and the leaked database does not record any civilian deaths in the logs of these incidents.

But the logs do reveal corroborating evidence, furnished at the time by US troops involved in the fighting, that the clinic was a target for shelling.

A surveillance unit reported that it "observed anti-Iraq forces unloading a vehicle at the clinic south of the Hydra mosque … Another vehicle arrived and an unidentified number of armed individuals exited the vehicle."

On that morning of 9 November the field reports describe heavy street fighting as the area is surrounded and the mosque captured. A detachment of the 1st Battalion 8th US Marines called in repeated heavy artillery strikes.

At 6.53am the marines' Bravo company, "heavily engaged" by machine-guns, rocket-propelled grenades and sniper fire, called in eight successive high explosive rounds from 155mm howitzers that landed in the mosque area.

The soldiers then signalled: "Battle damage assessment unknown." This is a frequent report about air and artillery strikes during the entire week of ferocious fighting.

At other times the troops record Iraqi deaths but invariably classify all the corpses as "enemy". When a helicopter gunship killed two Reuters journalists with a group of other men in a Baghdad street, in one notorious 2007 incident, all were listed as "enemy killed in action".

John Sloboda, IBC co-founder, has called for a British judicial inquiry into the civilian deaths, which he says have not been addressed by the Chilcot hearings. "If we try to hide the reality of what happened we are going to sow seeds of hatred among those whose trust we are trying to gain and in whose name we said we were doing all of this."