The Food and Drug Administration is warning nine companies to stop selling purported remedies for bird flu and other forms of influenza because they have not been approved by the agency.

"FDA is not aware of any scientific evidence that demonstrates the safety or effectiveness of these products for treating or preventing avian flu, and the agency is concerned that the use of these products could harm consumers or interfere with conventional treatments," the FDA said Tuesday in a statement.

The FDA sent warning letters to the nine companies saying they are presenting misleading and unproven claims. The companies have 15 days to respond.

Claims made by the companies about their treatments include phrases like "prevents avian flu," "a natural virus shield" and "kills the virus," the FDA said.

Because of these claims, the agency considers their products, most of which are marketed as dietary supplements, to be new drugs that require approval before they can be sold.

The nine companies are: Sacred Mountain Management Inc., BODeSTORE.com, Melvin Williams, iceland Health Inc., PolyCil Health Inc., PRB Pharmaceuticals Inc., Chozyn LLC, Vitacost.com and Healthworks 2000.