The ongoing unrest makes gathering information difficult

This is about a quarter of the figure given in a disputed Lancet article, but nearly three times higher than that of the Iraq Body Count campaigning group.

The result is based on interviews with over 9,000 families across Iraq carried out by the health ministry for the WHO.

The survey says more than half of all violent deaths were in Baghdad.

The World Health Organization study looks only at the period from March 2003 until June 2006.

Researchers interviewed households right across Iraq, in towns and the countryside, and asked the head of each one for details of all deaths in the group.

They say violence became a leading cause of death of Iraqi adults; among men between 15 and 59 it was the main cause of death.

Note of caution

The survey authors say they are confident in the general level of accuracy of the answers they received because they had a high response rate, and because the answers from other questions in their survey were consistent with information they already had.

Despite the large number of families interviewed, the authors do not say 151,000 is a precise figure.

The kind of scene that is played out many times a day in Iraq

Instead, they offer a range of between 104,000 and 223,000.

"Assessment of the death toll in conflict situations is extremely difficult and household survey results have to be interpreted with caution," said study co-author Mohamed Ali, a WHO statistician.

"However, in the absence of comprehensive death registration and hospital reporting, household surveys are the best we can do."

Difficulties facing those leading the survey included:

no central records are kept

some areas are too dangerous to visit

more people leave their homes in times of conflict

many people have left Iraq altogether

"The survey results indicate a massive death toll since the beginning of the conflict," said Iraqi health minister Salih Motlab al-Hasanawi.

The level of civilian casualties in Iraq has been a controversial issue ever since the US-led invasion of 2003.

US criticism

The US does not give estimates of civilian deaths, although President George W Bush once gave a figure of 30,000.

In October 2006, the Lancet published a study by the Johns Hopkins Bloomberg School of Public Health. It suggested that between about 655,000 more Iraqis had died since the invasion than would normally have been expected.

Its researchers spoke to more than 1,800 families comprising 12,800 people, comparing mortality rates in selected areas before and after the invasion.

It covered a similar period to the latest survey, but was undermined by allegations that the number of people surveyed was too small and that the authors may have inflated the figures for political reasons.

Mr Bush himself criticised its methodology as "pretty well discredited", and its figure as "not credible".

The best-known casualty tracker is the independent Iraq Body Count. It says it prefers to err on the side of caution, counting only confirmed deaths. The toll it gave for up to June 2006 was under 50,000.

It now gives a range of 80,381 - 87,792.

The BBC's Humphrey Hawkesley, reporting from Baghdad, says violence has fallen in recent months, put down to the success of the US's injection of extra troops.

But he says Iraq remains a very dangerous place.

The latest study's findings are published on the website of the New England Journal of Medicine.