Another company has joined a massive recall of pet food products,with the latestmove comingafter U.S. government testing found a chemical used to make plasticsin certainbrands byOntario-based Menu Foods Inc.

Hill's Pet Nutrition issuedits recall Friday forits Prescription Diet m/d Feline Dry food,which issold in Canada and the U.S.It's the first dry pet food to be recalled.

The announcementcame just hoursafter the U.S. Food and Drug Administration said that the tests detected melamine — used in the manufacture of plastics, laminates and fertilizer — in Menu Foods samples. It was also found inan ingredient, wheat gluten.

"Hill's is taking this precautionary action because during a two-month period in early 2007, wheat gluten for this product was provided by a company that also supplied wheat gluten to Menu Foods," the company said in a statement on its website.

Hill's, based in Topeka, Kan., said its other products were not affected.

Menu Foods issued the recall in mid-March amid reports that cats and dogs had died of kidney failure after eating its food. It said there had been 16 confirmed deaths of cats and dogs in the U.S., but none in Canada, while a U.S. veterinary website said it had heard of more than 100 deaths.

Chemical in cats' urine

At a news conference Fridayin Rockville, Md., FDA officials said Cornell University scientists, who conducted independent tests on the federal agency's behalf, also found melaminein the urine of sick cats andin the kidney of one cat that died after eating the company's wet food.

Stephen Sundlof, the director of the FDA's Center for Veterinary Medicine, said there was an "undeniable" connection between the melamine in the cats' urine and the melamine in the pet food.

But he added thattheFDA was not yet certain whether the melamine caused the pets' deaths, and it hasn't determined how the substance got into the pet food.

The FDA officials also said scientists were no longer investigating any connection between the deaths and the rat poison aminopterin.

Although it had been detected by independent labs in New York, the FDA said aminopterin had not been found in further testing.

The FDA said it also doesn't know how melamine got into wheat gluten, which is used as an ingredient in both dry and wet pet foods. But it has traced the tainted wheat gluten to a supplier from China. It is also working with one pet food maker to determine if any of that was used in its production of dry dog food, officials said.

In a separate news conference, Menu Foods chief executive Paul Henderson saidFriday it's still not clear how melamine found its way intoits pet foods. The contamination was discovered in wheat gluten provided by a new American supplier and has been discontinued, Henderson said.

He declined to name the supplier, saying U.S. authorities are still investigating, but said all products made since March 6 are safe.

Menu Foods hasfielded some 300,000 calls to its toll-free number, Henderson said.

So far, the FDA has received 8,800 complaints from vets and pet owners, but confirming that they're related to the Menu Foods tainted food will take time, officials said.

Animal rights group wants broader recall

The animal rights group People for the Ethical Treatment of Animals demanded earlier Friday that U.S. regulators expand a recall of nearly 100 brands of Menu Foods pet foods to also cover dry varieties.

The recall from Menu Foods — based in Streetsville just west of Toronto — requires stores to pull only the "wet" or "cuts and gravy" style of pet food packages from shelves. However, PETA members said they know of pet owners whose cats and dogs became sick after eating dry food.

The FDA told CBC News on Friday morning thatit had no plans to expand the recall to cover dry foods from the affected brands, which include Iams, Nutro and Eukanuba.

Officials from the agency said they had seen no indication thatanimals also fell ill from eating dry food.

Some pet owners grew concerned in February when they noticed their cats and dogs had suffered apparent kidney failure after eating certain packages of cuts and gravy food.

Last week, angry pet owners in Canada filed a $60-million second class-action lawsuit against Menu Foods Inc., alleging its products made their cats and dogs sick or killed them.

The Veterinary Information Network, a website representing 30,000 U.S. veterinarians and veterinary students, reported Tuesday that at least 471 cases of pet kidney failure have been reported since the recall, and more than 100 pets have died.

With files from the Associated Press and the Canadian Press