Tests on two brands of dog treats sold at Wal-Mart stores in the U.S. have shown the pet food contains traces of melamine — the same industrial chemical that caused an earlier recall of pet food products across North America in March.

Company spokeswoman Deisha Galberth said Tuesday that 17 tests confirmed the presence of the industrial chemical in Chicken Jerky Strips from Import-Pingyang Pet Product Co. and Chicken Jerky from Shanghai Bestro Trading. The pet food was not sold in Canada.

Customer complaints about the products prompted Wal-Mart to pull the product from its store shelves in the U.S. in July. Company officials said they did not issue a recall of the product until testing could be completed.

Galberth said the amounts of melamine were minimal and further tests were being conducted. U.S. consumers have been advised to return the affected products to the store for a refund.

The Wal-Mart announcement follows a massive pet food recall of more than 100 brands in March across North America traced back to tainted wheat gluten imported from China. Tests showed the wheat gluten was contaminated with melamine.

The U.S. Food and Drug Administration confirmed 16 animal deaths were related to the tainted pet food. The U.S. agency also fielded about 17,000 calls from consumers about the pet food recall.

With files from the Associated Press