John Simpson, (BBC), Fallujah: Six years after the intense fighting began in the Iraqi town of Fallujah between US forces and Sunni insurgents, there is a disturbingly large number of cases of birth defects in the town.

Fallujah is less than 40 miles (65km) from Baghdad, but it can still be dangerous to get to.

As a result, there has been no authoritative medical investigation, certainly by any Western team, into the allegations that the weapons used by the Americans are still causing serious problems.

The Iraqi government line is that there are only one or two extra cases of birth defects per year in Fallujah, compared with the national average.

'Daily cases' - But in the impressive new Fallujah General Hospital, built with American aid, we found a paediatric specialist, Dr Samira al-Ani, who told us that she saw two or three new cases every day.

Most of them, she said, exhibited cardiac problems.

When asked what the cause was, she said: "I am a doctor. I have to be scientific in my talk. I have nothing documented. But I can tell you that year by year, the number [is] increasing.”

The specialist, like other medical staff at the hospital, seemed nervous about talking too openly about the problem.

They were well aware that what they said went against the government version, and we were told privately that the Iraqi authorities are anxious not to embarrass the Americans over the issue.

There are no official figures for the incidence of birth defects in Fallujah.

The US military authorities are absolutely correct when they say they are not aware of any official reports indicating an increase in birth defects in Fallujah - no official reports exist.

Mothers warned - But it is impossible, as a visitor, not to be struck by the terrible number of cases of birth defects there.

We heard many times that officials in Fallujah had warned women that they should not have children.

We went to a clinic for the disabled, and were given details of dozens upon dozens of cases of children with serious birth defects.

One photograph I saw showed a newborn baby with three heads.

While we were at the clinic, people kept arriving with children who were suffering major problems - a little girl with only one arm, several children who were paralysed, and another girl with a spinal condition so bad I asked my cameraman not to film her.

At the clinic we were told that the worst problems were to be found in the neighbourhood of al-Julan, near the river.

This was the heart of the resistance to the Americans during the two major offensives of April and September 2004, and was hit constantly by bombs and shells.

River water.

We went to a house where three children, all under six, were suffering from birth defects.

Two boys were partially paralysed, and their sister clearly had serious brain damage.

Like all the other parents we spoke to, their mother had no doubt that the American attacks were responsible.

Outside, a man who had heard we were there had brought his four-year-old daughter to show us. She had six fingers on each hand, and six toes on each foot.

She was also suffering from a number of other serious health problems. The father told us that the house where they still lived had been hit by an American shell during the fighting in 2004.

There may well be a link with drinking-water, especially in al-Julan.

After the fighting was over, the rubble from the town was bulldozed into the river bank, and most people in this area get their water from the river.

The true causes of the problem, and the question of the effects of the weapons the Americans used, can be resolved only by a proper independent inquiry by medical experts.

And until the security situation in and around Fallujah improves, it will be difficult to carry that out.