Pet food that killed several animals and sparked a nationwide recall was contaminated with rodent poison, a spokeswoman for the New York state Department of Agriculture and Markets said Friday.

A spokeswoman did not identifying the chemical or its source, but ABC News reported that the chemical was aminopterin, which initially contaminated wheat imported from China.

The poisoned wheat protein was used by Canadian pet food maker Menu Foods in nearly 100 brands of dog and cat food sold throughout North America.

The deaths of animals fed certain pet foods prompted a major recall of 60 million cans and pouches of pet food produced by Menu Foods for store brands carried by Wal-Mart, Kroger, Safeway and other large retailers, as well as private labels like Iams, Nutro and Eukanuba.

It has been suspected that wheat gluten used in most of the wet ("cuts-and-gravy" style) food is to be blame for deaths of ten animals and possibly more. Several cats and dogs have had kidney failure and other symptoms.

Rodent poison aminopterin is illegal in the U.S. It inhibits the growth of malignant cells and is used as a cancer drug. It also suppresses the immune system. In high doses, the chemical is highly toxic.

State officials will be releasing laboratory findings later today.