WASHINGTON (Reuters Health) - Depleted uranium of the same type found in the US military's armor-piercing ammunition has been shown to cause cancer when implanted in the muscles of laboratory animals.

The study is the first of its kind to show that depleted uranium, or DU, can cause cancer in animals. Depleted uranium has been the source of a recent controversy centered mostly in Europe, where veterans' groups have blamed DU-containing rounds for leukemia and other illnesses in military personnel who handled munitions during the Balkans War.

But the study's investigator cautioned that his results do not yet prove that the radioactive metal is dangerous to humans, or that the type of exposure the experimental rats received is analogous to exposure soldiers may have received in the Balkans.

``It's a warning flag that says we shouldn't ignore this. It doesn't mean that (DU) is carcinogenic to humans,'' Fletcher F. Hahn, a senior scientist at the Lovelace Respiratory Research Institute in Albuquerque, New Mexico, told Reuters Health.

Hahn and his research team implanted pellets containing 99.25% depleted uranium and 0.75% titanium into the muscles of experimental rats. The combination is identical to the alloy the military uses in its armor-piercing rounds. They implanted a second group of rats with non-radioactive metal pellets to serve as ``controls,'' and injected a third group with a different radioactive suspension.

The investigators found that the soft-tissue sarcomas, a form of cancer, were significantly more likely to occur in the muscles of animals that received the DU-containing implants than in control animals.

``The greater the size of the pellets, the greater the number of tumors produced,'' Hahn said during an interview at a research forum on Gulf War illness sponsored by the Department of Defense (news - web sites), the Department of Veterans Affairs, and the Department of Health and Human Services (news - web sites).

The researchers performed the study with a grant from the US Army, which is concerned about the possible effects of depleted uranium once it is inside the body in solid form. As many as 62 American soldiers were wounded with shrapnel from DU rounds when their tanks or Bradley armored vehicles were hit by friendly fire during the Gulf War.

That is not the same kind of exposure that has caused controversy in Europe over the past month. There, researchers and veterans are concerned about possible cancers resulting from either handling DU rounds or from inhaling radioactive dust left after rounds penetrate armor and vaporize.

So far none of the American men hit with shrapnel has developed cancer, Hahn said. The Army will give his research group $400,000 to $500,000 over the next 2 years to look into the possible mechanisms of DU-induced sarcomas in the animals, he said.