WASHINGTON - An industrial chemical that led to a nationwide recall of more than 100 brands of cat and dog foods has been found to contaminate a second pet food ingredient, expanding the recall further.

The chemical, melamine, is believed to have contaminated rice protein concentrate used to make a variety of Natural Balance Pet Foods products for both dogs and cats, the Food and Drug Administration said Wednesday. Previously, the chemical was found to contaminate another ingredient, wheat gluten, used by at least six other pet food and treat manufacturers.

Natural Balance said it was recalling all its Venison and Brown Rice canned and bagged dog foods, its Venison and Brown Rice dog treats and its Venison and Green Pea dry cat food.

The Pacoima, Calif., company said recent laboratory tests showed the products contain melamine. It believes the source of the contaminant was rice protein concentrate, which the company recently added to the dry venison formulas. Natural Balance does not use wheat gluten, which was associated with the previous melamine contamination, it said.

Last month, Menu Foods recalled 60 million cans of dog and cat food after the deaths of 16 pets, mostly cats, that ate its products. The FDA said tests indicated the food was contaminated with melamine, used in making plastics and other industrial processes. Five other companies later recalled pet products also made with wheat gluten tainted by the chemical.

The FDA has since blocked Chinese imports of wheat gluten. An FDA spokeswoman did not immediately return messages left seeking comment.