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The possibility of tampering in pet food blamed for the deaths and illness of animals in the U.S. and Canada is remote, officials with Menu Foods said Friday, after it was confirmed that a toxic substance had been found in their products.

Chief executive of Mississauga, Ont.-based Menu Foods, Paul Henderson, said that officials had identified that the products being recalled are from two U.S. manufacturing facilities.

The two plants where the tainted "cuts and gravy" style food came from are still in operation, Henderson said. They are located in Emporia, Kan., and Pennsauken, N.J.

When asked whether the firm would provide compensation for medical bills for sick pets, Henderson said "to the extent that we identify that the cause of any expenses incurred are related to the food, Menu will take responsibility for that."

However, the company was not yet certain how a toxic subtance had made its way into the pet food.

"How did this substance get in to our products? At this stage, we don't know," Henderson said.

Henderson told reporters that the company will begin testing all suspect raw materials through a process of elimination but denied that Menu Foods had been negligent.

"Some raw material has entered our supply chain that did not meet the quality that had been represented," Henderson told reporters at an afternoon press conference in Toronto.

He also sought to reassure the public that there was no reason to suspect the contamination affected any products beyond the ones identified in the recall.

The company had spoken to nearly 200,000 consumers, Henderson said.

"They are scared. Some of them, like myself, are angry,'' Henderson said. "We are grateful for their patience.''

Earlier in the day, New York state officials said that traces of aminopterin, an ingredient used in rat poison, were found in tests of food samples suspected of causing kidney failure in cats and dogs.

Officials from the New York State Department of Agriculture confirmed reports that rat poison has been found in pet food products blamed for the deaths and illnesses of as many as 16 animals in the U.S. and Canada.

State agriculture commissioner Patrick Hooker said tests are now being conducted on individual materials in the pet food.

"This is a long step in a process that will lead us to know what has happened and how it has happened," Hooker said.

Aminopterin, now banned in the U.S., has been used as a cancer treatment drug, an abortive and a rat poison.

The U.S. Food and Drug Administration has said the investigation into the pet deaths focused on wheat gluten imported from China.

Wheat gluten itself would not cause kidney failure, but a common ingredient could have been contaminated, the FDA said.

A Friday report from ABC News stated that the rodenticide had been used on wheat that was imported from China by Menu Foods.

The pet food company then used the grain in close to 100 brands of dog and cat food.

New York Agriculture Commissioner Patrick Hooker, and representatives from Cornell University's diagnostic lab said that information was beyond the scope of their investigation, and it would be up to Menu Foods to determine the source of the poison.

They confirmed the toxic substance had been identified in the pet food, but said they were far from learning how it go there.

The scientists have not yet determined how much poison made it into the supply, but said they have come up with a minimum amount of 40 parts per million.

There have been varying reports about the number of pets that have died as the result of eating contaminated food. The scientists wouldn't give an estimate, but when pressed by a reporter, Dr. Donald Smith said "based upon what we've heard in the last couple of days, 16 seems like a low number."

Experts say the effects of the poison could be reversed once the type and source of the toxin are confirmed.

"It is possible to get injections of folic acid which could potentially reverse the harmful effects," veterinarian Bernie Caplan said.

Last week, Menu Foods ordered a recall of the affected products in Canada and the U.S. after receiving reports that dogs and cats were becoming sick, and in some cases dying.

The massive recall affected roughly 60 million cans and pouches of pet food, sold under 91 brand names such as Iams and Eukanuba, and through major retailers including Safeway, Wal-Mart and PetSmart.

Meanwhile, a national class-action lawsuit has been launched in an Ontario court on behalf of pet owners who purchased the affected products.

The claim is seeking compensation for anyone who purchased products that were manufactured at the company's Emporia, Kan. plant between Dec. 3, 2006, and March 6.

The lawsuit alleges the company failed to implement proper quality control measures and testing before bringing the products into Canada.

Henderson told The Canadian Press the company first received reports of illnesses and deaths due to kidney failure in late February when customers began reporting problems.

Later, during testing this month, the company was notified that some of the animals had become sick from the "cuts-and-gravy'' style food, which prompted the investigation.

The company estimates the recall could cost as much as $40 million.

With a report from CTV's Denelle Balfour