The U.S. Food and Drug Administration warned General Mills Inc. (GIS) that the labeling for Cheerios whole-grain oat cereal contained "serious violations" of agency rules.

In a May 5 warning letter sent to the company and posted on the FDA's Web site Tuesday, the agency said the health claims made on the product's label about Cheerios' ability to lower cholesterol cause the product to be a drug under agency regulations.

The FDA said claims made on the product's package stating that Cheerios is clinically proven to lower cholesterol can only be made if the product were to be approved as a drug. The product label says Cheerios can lower "bad" cholesterol by 4% and cited a clinical study involving the product as part of a diet low in saturated fat and cholesterol. The FDA said Cheerios "can't be legally" marketed with claims it lowers cholesterol by a certain percentage without an approved new drug application.

A General Mills spokesperson wasn't immediately available to comment on the letter.

The FDA said General Mills must "promptly" correct the violations outlined in the letter, otherwise the agency could take enforcement action such as seizing products.

-By Jennifer Corbett Dooren, Dow Jones Newswires; 202-862-9294; jennifer.corbett@dowjones.com