World health experts have condemned the US and UK governments as "wholly irresponsible" for not setting up their own count of Iraqi civilian deaths.
Iraq health ministry casualty figures are misleading, campaigners say
In a statement published by the British Medical Journal (BMJ), the experts call on the US and UK immediately to launch a full, independent inquiry.
They say more accurate information is needed to "save lives in future".
The UK Foreign Office says figures from the Iraqi Ministry of Health are the most reliable available.
But the 24 health experts calling for an inquiry - from the US, UK, Australia, Spain, Italy and Canada - argue the Iraqi ministry sources are "likely seriously to underestimate casualties".
Their statement is the latest protest triggered by a critical report in medical journal the Lancet last October, which suggested 100,000 Iraqi civilians may have died since the March 2003 invasion.
The UK and US authorities dismissed that report as based on only a small sample of 988 Iraqi households.
The Iraqi figures they use show only 5,144 Iraqi civilians killed and 19,387 injured between April 2004 and 31 December 2004, the UK Foreign Office says.
These figures do not take into account deaths in the first 12 months after the US-led invasion, and include only violent deaths recorded through the health system.
The Iraq Body Count, a non-governmental database, currently puts the death toll at between 16,231 and 18,509 since March 2003.
"We believe the joint US/UK failure to make any effort to monitor Iraqi casualties is, from a public health perspective, wholly irresponsible," the experts' BMJ statement says.
"Counting casualties can help to save lives both now and in the future... We have waited too long for this information."
Prof Klim McPherson, of Oxford University, told the BBC News website the US and UK governments "ought to know the consequences" of the Iraq war.
There are no official figures for the period during the war
He criticised the Foreign Office for dismissing the figures reported in the Lancet without coming up with any credible alternative.
Dr Bob Musil, of the US-based Physicians for Social Responsibility, accused the US government of deliberately giving out misleading lower, Iraqi figures to keep the real scale of civilian casualties hidden.
"We consider it both irresponsible and unethical - frankly, we have a responsibility to let people know what's going on from American actions," he told the BBC.
He accused the US government of sidelining the Lancet report because "it would stir up further opposition to the war".
"That is politicising public health and we think that's outrageous," he said.
Dr Musil warned that failing to repair Iraq's damaged medical infrastructure was storing up trouble for the future.
Cambridge-based Prof Sheila Bird, who also backed the BMJ statement, called for the UK government to allow public health scientists to work alongside the Ministry of Defence to interpret data and save lives.
A Foreign Office spokesman told the BBC the UK government did not agree with the need for an independent inquiry into casualty figures.
He said: "The government has made clear that it believes in the importance of Iraqi lives but it also believes that in the current difficult circumstances the kind of survey proposed is not feasible and would not provide reliable data."
Dr Musil warns failure to repair hospitals may cause problems
Responsibility for counting the dead in Iraq lay with the Iraqi authorities, he said.
The Pentagon was not able to comment.
Hamit Dardagan, co-founder of the Iraq Body Count project, told the BBC that February 2005 was probably the worst month for civilian casualties since US President George W Bush declared the war over in May 2003.
He rejected the Foreign Office view that it was too dangerous to carry out casualty studies.
If official support was provided "there would be no question that it could be done" by Iraqi medical professionals, he said.
"Are they saying that Iraq is in such a state that people cannot knock at their houses and interview them?" he asked.
"I think if the will is there, it can be done."