Newly leaked documents on the U.S.-led invasion of Iraq suggest 15,000 more civilians have been killed since 2004 than previously thought, highlighting the difficulty of tracking the war's true cost to human life.

In a move that left U.S. officials fuming, the website WikiLeaks published nearly 400,000 U.S. military documents Friday that offer details about the Iraq war, including tens of thousands of civilian deaths.

WikiLeaks staffers conferred with Iraq Body Count, a private British group that monitors civilian deaths in Iraq, to reach its tally of 15,000 previously unknown deaths.

The organization's civilian death toll had been at 107,369. The new figures would push that to more than 122,000.

"That tremendous scale should not make us blind to the small human scale that occurs in this material," WikiLeaks founder Julian Assange told reporters Saturday in London. "In fact, it is the deaths of one and two people per event that killed the overwhelming number of people in Iraq."

The documents, which include field reports from low-ranking soldiers and intelligence officers in Iraq, also suggest U.S. forces did not probe allegations that Iraqi soldiers tortured or killed insurgents they took prisoner.

But Iraqi Prime Minister Nouri al-Maliki denied any proof that Iraqi forces mistreated detainees under his watch.

U.S. officials denounced WikiLeaks' latest move, just as they condemned the site for previous leaks of military records pertaining to the war in Afghanistan, citing increased risks to U.S. troops and civilians overseas.

However, the Pentagon has never confirmed the authenticity of documents published on the WikiLeaks website, and has also never indicated the information is inaccurate.

Figures on civilian deaths in Iraq vary widely. The Iraqi government says at least 85,694 civilians and security officials were killed between January 2004 and Oct. 31 2008. Last July, the U.S. military released figures that suggest nearly 77,000 civilians and security forces were killed between Jan. 2004 and Aug. 2008, the bloodiest period of the insurgency.

While U.S. officials have downplayed suggestions of a civil war marked by revenge killings and mob-style violence, the newly published reports suggest that most Iraqis died at the hands of their fellow countrymen -- a disturbing but not unexpected contention that reveals the sectarian nature of the conflict.

The documents, some of which have names or other identifying information blacked out, come out as the U.S. military prepares to withdraw its remaining 50,000 troops from Iraq by the end of next year.

Phillip McDowell, a former U.S. soldier now living in Canada as a war resister, said the release of the documents shows that the U.S. government has not been truthful about Iraq.

In particular, McDowell said indications of torture and prisoner abuse were apparent during his own time in Iraq as a soldier.

"These documents coming out now are just shedding light and really exposing the truth of what has happened," he told CTV News Channel Saturday.

After serving in the war, McDowell refused to be redeployed to Iraq.

He said that the torture and mistreatment documented in the leaked documents were "systematic" during the war.

"It's a good thing (the documents) are coming out, so people can see the truth as to what happened."

Not only do the reports show that the war was bloody and brutal, but they reinforce the false nature of the conflict, which was predicated on the mistruth that Saddam Hussein had weapons of mass destruction, McDowell said.

"This war was based on lies and now we have proof to the outcome of this."

With files from The Associated Press