The UN Environment Program has trained Iraqi specialists in detoxification, but says any clean-up could cost up to $40m (£23m).

Chemical spills, unsecured hazardous material and widespread pollution by depleted uranium are among the issues.

Without clean-up, heavy metals can poison ground water, causing illness.

The Unep has examined five sites as part of its training efforts, and is concerned by the results.

"There are hundreds, probably thousands of other sites with the need of assessment," said Mural Thummarukudy, Unep's manager in Iraq, who appealed for donations.

String of wars

Among the five sites already probed are a metal plating facility at al-Qadyissa that was bombed, looted and then demolished in 2003.

Several tons of cyanide remain on the site, which is now an unsecured area used as a playground by local children.

The other sites include an old sulphur mine, a munitions factory containing unexploded ordnance and an abandoned petrochemicals plant.

Narmin Othman, Iraq's environment minister, said that some 311 sites were polluted by depleted uranium, the Associated Press reported.

Many of Iraq's potential danger spots were either damaged or destroyed during the Iran-Iraq war of the 1980s, the 1991 Gulf war or the US-led invasion in 2003.

In addition, many of the sites have been looted in recent years as insurgents and militias raid them for weapons and materiel, with little thought for potential environmental effects.