An average of 120 Iraqi adults died a violent death every day in the three years following the US-led invasion of March 2003, the World Health Organisation (WHO) said Wednesday.
A household survey carried out by the WHO and the Iraqi government between March 2003 and June 2006 estimated that between 104,000 and 223,000 people died from violence during that period.
"Violence became a leading cause of death for Iraqi adults and the main cause for men aged 15-59 years," according to the study which appeared on the website of the New England Journal of Medicine.
More than half of all the violent deaths occurred in the capital Baghdad, it added.
The WHO estimated the daily death toll by averaging the overall estimates out at 151,000 dead. The survey was based on interviews conducted in 9,345 households in nearly 1,000 neighbourhoods and villages across Iraq.
"Assessment of the death toll in conflict situations is extremely difficult and household survey results have to be interpreted with caution," said WHO statistician and study co-author Mohamed Ali.
The US military has never given any estimates of civilian casualties, and other studies have given wildly varying figures.
"Our survey estimate is three times higher than the death toll through careful screening of media reports by the Iraq Body Count project," said Naeema Al Gasseer, the WHO representative in Iraq.
In 2006, another study by US doctors in the British medical journal The Lancet claimed that 655,000 Iraqis had died as a result of the invasion to topple Saddam Hussein.