In a letter addressed to Coca-Cola, the Food and Drug Administration said the beverage company placed inappropriate nutritional claims on its Diet Coke Plus soft drink.

Federal regulators issued a warning to the Coca-Cola Company regarding the label of one of its drinks, which violates the agency’s guidelines for using the term "plus" and claiming that it is a source of vitamins and minerals.

It is true that the “misbranded” product contains zinc, magnesium and vitamin B, the FDA says, but these amounts are unquestionably insufficient to make the claims. The letter, issued on Dec. 10, and posted on the FDA website on Tuesday two weeks later, also wrote that foods labeled "plus" ought to have at least 10 percent more nutrients than comparable items.

According to an e-mail written by Scott Williamson, a Coca-Cola North America spokesman, the soft drink giant takes the matter seriously. "This does not involve any health or safety issues, and we believe the label on Diet Coke Plus complies with FDA policies and regulations." Williamson added that the Food and Drug Administration gave Coca-Cola 15 days to reply with its plans for actions, and that the company plans to do that in early January.

The drink was released in the UK in October 2007, available in two variants, one with vitamins B3, B12, and vitamin C, and the other one containing antioxidants with extra green tea and vitamin C.

The world’s largest soft-drink maker fell 69 cents to $43.97 at 4 p.m. in New York Stock Exchange composite trading.