Recalled pet foods produced by Canadian company Menu Foods contained a chemical used to make plastics, federal officials said Friday.

The Food and Drug Administration said it found melamine in samples of the Menu Foods pet food, as well as in wheat gluten used as an ingredient.

Scientists also have found the chemical in the urine of sick cats, as well as in the kidney of one cat that died after eating the company's wet food.

Melamine is typically used to produce plastic kitchen wares. It's apparently used as a fertilizer in Asia. After the recall Menu Foods said they started using wheat gluten from the new supplier in China.

Government tests failed to confirm the presence of rat poison, which was previously reported as a possible cause of death of several animals. Earlier this month, New York State Food Laboratory identified a rat poison and cancer drug called aminopterin in pet food.

Menu Foods recalled 60 million containers of cat and dog food earlier this month after animals died of kidney failure after eating the Canadian company's products. The recall involved nearly 100 brands of "cuts and gravy" style dog and cat food made by Menu Foods.

Menu Foods used wheat gluten, a source of vegetable protein, to thicken the gravy of its pet foods, FDA officials have said.

It is not clear how many pets may have been poisoned by the apparently contaminated food, although reports suggest hundreds if not thousands have died. There is no risk to human food, Patrick Hooker, commissioner of the New York state Department of Agriculture and Markets, told reporters.

The FDA alone has received more than 8,000 complaints since the recall was announced.