It played unwilling host to one of the bloodiest battles of the Iraq war. Fallujah's homes and businesses were left shattered; hundreds of Iraqi civilians were killed. Its residents changed the name of their "City of Mosques" to "the polluted city" after the United States launched two massive military campaigns eight years ago. Now, one month before the World Health Organisation reveals its view on the legacy of the two battles for the town, a new study reports a "staggering rise" in birth defects among Iraqi children conceived in the aftermath of the war.

High rates of miscarriage, toxic levels of lead and mercury contamination and spiralling numbers of birth defects ranging from congenital heart defects to brain dysfunctions and malformed limbs have been recorded. Even more disturbingly, they appear to be occurring at an increasing rate in children born in Fallujah, about 40 miles west of Baghdad.

There is "compelling evidence" to link the increased numbers of defects and miscarriages to military assaults, says Mozhgan Savabieasfahani, one of the lead authors of the report and an environmental toxicologist at the University of Michigan's School of Public Health. Similar defects have been found among children born in Basra after British troops invaded, according to the new research.

US marines first bombarded Fallujah in April 2004 after four employees from the American security company Blackwater were killed, their bodies burned and dragged through the street, with two of the corpses left hanging from a bridge. Seven months later, the marines stormed the city for a second time, using some of the heaviest US air strikes deployed in Iraq. American forces later admitted that they had used white phosphorus shells, although they never admitted to using depleted uranium, which has been linked to high rates of cancer and birth defects.

The new findings, published in the Environmental Contamination and Toxicology bulletin, will bolster claims that US and Nato munitions used in the conflict led to a widespread health crisis in Iraq. They are the latest in a series of studies that have suggested a link between bombardment and a rise in birth defects. Their preliminary findings, in 2010, prompted a World Health Organisation inquiry into the prevalence of birth defects in the area. The WHO's report, out next month, is widely expected to show an increase in birth defects after the conflict. It has looked at nine "high-risk" areas in Iraq, including Fallujah and Basra. Where high prevalence is found, the WHO is expected to call for additional studies to pinpoint precise causes.

The latest study found that in Fallujah, more than half of all babies surveyed were born with a birth defect between 2007 and 2010. Before the siege, this figure was more like one in 10. Prior to the turn of the millennium, fewer than 2 per cent of babies were born with a defect. More than 45 per cent of all pregnancies surveyed ended in miscarriage in the two years after 2004, up from only 10 per cent before the bombing. Between 2007 and 2010, one in six of all pregnancies ended in miscarriage.

The new research, which looked at the health histories of 56 families in Fallujah, also examined births in Basra, in southern Iraq, attacked by British forces in 2003. Researchers found more than 20 babies out of 1,000 were born with defects in Al Basrah Maternity Hospital in 2003, a number that is 17 times higher than recorded a decade previously. In the past seven years, the number of malformed babies born increased by more than 60 per cent; 37 out of every 1,000 are now born with defects.

The report's authors link the rising number of babies born with birth defects in the two cities to increased exposure to metals released by bombs and bullets used over the past two decades. Scientists who studied hair samples of the population in Fallujah found that levels of lead were five times higher in the hair of children with birth defects than in other children; mercury levels were six times higher. Children with defects in Basra had three times more lead in their teeth than children living in non-impacted areas.

Dr Savabieasfahani said that for the first time, there is a "footprint of metal in the population" and that there is "compelling evidence linking the staggering increases in Iraqi birth defects to neuro-toxic metal contamination following the repeated bombardments of Iraqi cities". She called the "epidemic" a "public health crisis".

"In utero exposure to pollutants can drastically change the outcome of an otherwise normal pregnancy. The metal levels we see in the Fallujah children with birth defects clearly indicates that metals were involved in manifestation of birth defects in these children," she said. "The massive and repeated bombardment of these cities is clearly implicated here. I have no knowledge of any alternative source of metal contamination in these areas." She added that the data was likely to be an "underestimate", as many parents who give birth to children with defects hide them from public view.

Professor Alastair Hay, a professor of environmental toxicology at Leeds University, said the figures presented in the study were "absolutely extraordinary". He added: "People here would be worried if there was a five or 10 per cent increase [in birth defects]. If there's a fivefold increase in Fallujah, no one could possibly ignore that; it's crying out for an explanation as to what's the cause. A rapid increase in exposure to lead and mercury seems reasonable if lots of ammunition is going off. I would have also thought a major factor would be the extreme stress people are under in that period; we know this can cause major physiological changes."

A US Defense Department spokesperson said: "We are not aware of any official reports indicating an increase in birth defects in Al Basrah or Fallujah that may be related to exposure to the metals contained in munitions used by the US or coalition partners. We always take very seriously public health concerns about any population now living in a combat theatre. Unexploded ordnance, including improvised explosive devises, are a recognised hazard."

A UK government spokesperson said there was no "reliable scientific or medical evidence to confirm a link between conventional ammunition and birth defects in Basra", adding: "All ammunition used by UK armed forces falls within international humanitarian law and is consistent with the Geneva Convention."

Dr Savabieasfahani said she plans to analyse the children's samples for the presence of depleted uranium once funds have been raised. She added: "We need extensive environmental sampling, of food, water and air to find out where this is coming from. Then we can clean it up. Now we are seeing 50 per cent of children being born with malformations; in a few years it could be everyone."

Metal hazards

Lead

Throughout pregnancy, lead can pass from a woman's bones to her child; the levels of lead in maternal and foetal blood are almost identical. Children and particularly the unborn are more susceptible to lead than adults. At high levels of exposure, lead attacks the brain and central nervous system, causing comas, convulsions and even death, according to the WHO. Children who survive acute lead poisoning are typically left with mental defects and behavioural problems.

Mercury

Exposure to metallic, inorganic or organic mercury can permanently damage the brain, kidneys and developing foetus. Mercury can enter the air, water and soil. Its harmful effects can be passed from mother to the unborn child, leading to brain damage, mental defects, blindness, seizures, muteness and lack of co-ordination.

Depleted uranium