War's effects on health can be much harder to identify than death and horrendous physical injuries. The US department of veterans affairs recently accepted that Vietnam war veterans may have developed B cell leukaemias, Parkinson's disease and ischemic heart disease as a result of exposure to a blend of herbicides known as Agent Orange, a defoliating agent sprayed by US warplanes to deprive their enemies of cover.

Similarly, ionising radiation from the atomic bombs dropped on Hiroshima and Nagasaki in 1945 led to medical complications such as cancers, nausea, hair loss, bleeding into the skin, inflammation of the mouth and throat and birth defects.

Professor Nigel Brown, an expert in the causes of birth defects and dean of the faculty of medicine and biomedical science at St George's, University of London, points out that war zones such as Falluja involve many of the risk factors that cause deformities in children.

"The whole of the war situation produces a very unusual set of circumstances to which the civilian population is exposed, mainly involving the destruction of the built environment and its knock-on effects," he said.

"Those include the degrading of sanitation, the stress [on people of being in a place of conflict], the disruption of the water supply, poor nutrition and air pollution caused by both chemicals and particulates."

It was impossible to identify any one of those particular factors that may lie behind the apparent dramatic increase of birth defects in Falluja.

In addition, despite suspicion to the contrary, there is no reliable evidence to show that the components of munitions causes birth defects, except for ionising radiation, Brown said.

Some American service personnel who had seen action in Vietnam and the first Gulf war believed those conflicts caused them to have children with serious malformations. However, when their concerns were investigated, no proof was found. But studies in this area have concentrated on the health of combatants and their offspring and not on civilians caught up in conflicts, so evidence is very limited.

But what of white phosphorus, which was used in Falluja in 2004? No studies have been done, among either combatants or civilians, so it is impossible to link it to the abnormalities.

"These birth defects in Falluja could be the result of multiple factors including the sheer psychological stress on the local population of being in a war zone, malnutrition, air and water pollution and a cocktail of chemicals, which may include contamination from munitions," said Brown.

Birth defects range from minor ailments, such as a discolouration of the skin, to life-threatening conditions such as hydrocephalus and spina bifida. In most countries between 2% and 3% of all babies born have some form of birth defect. However, only between 1% and 10% of those involve a neural tube defect, which are the most debilitating and likely to lead to death.

"If neural tube defects are occurring apparently quite frequently in Falluja now that would be a dramatic increase over the expected rate for what are, in normal circumstances, rare events and that would be a matter of considerable concern," said Brown.