LONDON -- The possibility that U.S. tank-piercing ammunition used in the Balkans wars contained more than just depleted uranium has prompted scientists to re-examine their skepticism about health risks to veterans.

    Experts' opinions that cancer cases reported by European veterans were not linked to depleted uranium assumed the material came from raw ore. But now the Pentagon says shells used in the 1999 Kosovo conflict were tainted with traces of plutonium, neptunium and americium -- byproducts of nuclear reactors that are much more radioactive than depleted uranium.

    "If it has been through a reactor, it does change our idea on depleted uranium," said Michael Repacholi, the World Health Organization's radiation expert. "It all depends on the amounts."

    The main new concern, experts say, is plutonium, a highly toxic radioactive metal.

    On Thursday, NATO Secretary-General Lord Robertson reiterated NATO's position that Balkans peacekeepers have not been shown to suffer health damage from depleted uranium ammunition. U.S. officials have said the shells contained mere traces of plutonium, not enough to cause harm.

    But WHO experts asked the U.S. government this week to clarify exactly how much plutonium and other radioactive material was in the ammunition.

    Countries that sent peacekeepers to Bosnia and Kosovo have been looking for links between the depleted uranium ammunition and illnesses contracted by veterans. A wave of fear swept across Europe and beyond after Italy announced it was screening its soldiers because 30 Balkans veterans had become ill, including five who died of leukemia.

    Scores of countries began testing soldiers for radiation poisoning. The WHO expects to start new studies in the next six months.

    Experts must first establish whether cancers are more common than normal among troops before they go on to investigate why. So far, there is no confirmed increase in cancer rates, said WHO's Repacholi.

    Lung cancer is the main danger from the radiation, but experts say it takes several decades for lung cancer to develop from radiation exposure.

    It is just about possible for leukemia cases to start showing up two years after exposure to radiation, but they are less likely to occur than lung cancer and it would take a massive dose, experts say.

   Uranium that goes through a nuclear processing plant splits into several substances, including depleted uranium-238, plutonium and other radioactive wastes. If the elements are not separated properly, the depleted uranium can be contaminated. It is unclear where the depleted uranium in the Kosovo weapons came from.