The U.S. Food and Drug Administration (FDA) is warning consumers not to buy or use fraudulent cancer "treatments" available on the Internet that come in many forms, including pills, tonics, and creams and are sold under various names.

The federal agency has sent letters warning more than two dozen companies to stop selling false products that claim to prevent or cure cancer. Medicinal products and devices intended to treat cancer must gain FDA approval before they are marketed, the agency said Tuesday.

The agency said it had no confirmed reports of death associated with the products, but said their use poses both direct and indirect health threats to consumers by delaying or interfering with proven, beneficial treatments.

On Tuesday, the federal agency ordered 23 U.S. companies and one Canadian and one Australian company, to stop selling certain cancer cures on the Internet or they may have to face regulatory actions like product seizure or criminal prosecution.

The warning is aimed at 125 unapproved products with labeling claims to cure, treat or prevent cancer. The bogus cures include ingredients such as bloodroot, shark cartilage, coral calcium, cesium, ellagic acid, Cat's Claw, an herbal tea called Essiac, and mushrooms such as Agaricus Blazeii, Shitake, Maitake, and Reishi, the FDA said.