TAMPA, Fla. (AP) _ The Food and Drug Administration is investigating complaints that products being sold as 100 percent apple juice were actually diluted with sugar water.

The agency announced the investigation Monday, nearly a week after the maker of Minute Maid juices sued six suppliers of apple juice concentrate in Tampa federal court, claiming they sold diluted products.

The FDA said other juice brands are also affected. Minute Maid is withdrawing all its 100 percent juice products containing apple juice from warehouses, but isn't pulling the products from grocery store shelves because they're safe to drink.

The sugar is a form of the fructose found in all fruits, FDA Deputy Commissioner Mary Pendergast said. Not enough was added to the juice to significantly deplete its nutrient value, she said.

However, 100 percent juice products are generally more expensive than others so consumers weren't getting what they paid for.

The FDA said U.S. apple juice sellers, who paid $10 a gallon for 100 percent concentrate only to get the equivalent of 90 percent juice, were defrauded by their juice suppliers. The price of European concentrate doubled last year after a bad apple crop.

The FDA would not say which companies it is investigating, but said this form of fructose, known as hydrolyzed inulin syrup, is made only in northern Europe. It is derived from such plants as asparagus or chicory.

Coca-Cola Foods, makers of the Minute Maid brand, filed a lawsuit last week seeking a refund and damages for apple juice concentrate it says was fraudulently supplied by a group of European and U.S. companies.

According to the lawsuit, more than 417,000 gallons of concentrate shipped last year to Coca-Cola's purchasing office in Auburndale, Fla, about 45 miles east of Tampa, contained a sweetener derived from an extract of chicory or Jerusalem artichoke known as fructuline.

As a result, the Atlanta-based Coca-Cola Co. has stopped production and shipment of products containing apple juice and has lost an unspecified sum in profits, according to the lawsuit.

Defendants in the case include Empresa Commercial Internacional De Frutas S.A. of Lichtenstein, Apul Fruitconsult AG of Switzerland, Corronade International Trading Limited of Switzerland, Atlanta Corp. of New York, Pittra Inc. of New York and G.B. International Inc. of New Jersey.

The FDA said it learned of the problem a month ago when a scientist who was developing a test for juice ingredients told the agency. Apple juice makers independently discovered the fructose a few days later.

Apple juice specially made for infants was not affected, Pendergast said.