WASHINGTON -- The head of the company at the center of a massive pet food recall said the firm can't explain why some cats and dogs have developed acute kidney failure and died.

At least 16 animal deaths -- 15 cats and one dog -- led to the recall of 60 million cans and pouches of pet food sold throughout North America under 95 brand names. Menu Foods president Paul Henderson called the deaths "a puzzling and troubling experience." He said the food shows no sign of contamination.

Henderson told The Associated Press that his company is looking at a single ingredient, but he wouldn't identify it.

The Food and Drug Administration has said the investigation is focusing on wheat gluten, a source of protein and a thickener. The FDA said wheat gluten itself would not cause kidney failure, but could have been contaminated by heavy metals or mold toxins.

Wheat gluten, a protein source, is commonly used as filler. Menu Foods said the products were made with wheat gluten from a new supplier. That supplier has been replaced.

The recall includes "cuts and gravy" style dog and cat food produced at Menu Foods' facility in Emporia, Kan., between Dec. 3, 2006, and March 6, 2007. The products are distributed by major retailers such as Wal-Mart, Kroger and Safeway.

A complete list of the recalled products along with product codes, descriptions and production dates is available from the Menu Foods Web site at menufoods.com.

Officials are warning pet owners to immediately stop feeding the contaminated foods to their pets and said owners should see their pets' veterinarians if they develop signs of kidney failure, including loss of appetite, vomiting or lethargy.

Woman Sues, Seeks Class-Action Status

A Chicago woman has sued Menu Foods, claiming the pet-food manufacturer delayed announcing a recall of 60 million containers of dog and cat food despite knowing its products were contaminated and potentially deadly.

Dawn Majerczyk said her cat, Phoenix, fell sick last week just two days after he ate a single package of Special Kitty -- one of 95 cat and dog food brands recalled by Menu Foods.

Majerczyk said she took the cat to the vet the day of the recall. She said the cat had lost 6 pounds in four days and was lethargic, dehydrated and nearly blind. She returned over the weekend to have him put down after his organs began to fail.

Her suit seeks class-action status.