WASHINGTON (Reuters) - The U.S. Food and Drug Administration on Friday said it is conducting an investigation into the deaths and illnesses of dogs who consumed food made by the privately owned Diamond Pet Foods. The Meta, Missouri-based maker of premium pet food, sold under labels that include Diamond, Country Value and Professional, last week said it discovered the toxin aflatoxin in products made at its Gaston, South Carolina, plant. "Customers who have purchased the recalled Diamond Pet Food manufactured in the South Carolina plant should immediately stop using it and return any remaining product to their retailer," the FDA said in a statement. Aflatoxin comes from a fungus and develops on crops during hot weather and drought. It was detected in several key growing states including Iowa and Illinois this year. Large quantities can cause cancer in humans, and it can be deadly to animals. In its statement, the FDA said that some of the recalled product was exported to at least 29 countries including countries in the European Union. "These countries have been notified," the FDA said. Earlier this week, Diamond Pet Foods opened a special customer information center in response to the recall. "We're committed to providing the most up-to-date information we receive, and will take aggressive steps to help our customers, retailers and distributors," said Diamond's general manager Mark Brinkmann. In a comments made last week, Brinkmann said the company had received a call from a customer in New York whose dog had died, which then prompted the company to test samples from its South Carolina plant. The company routinely pulls samples every 30 minutes, and was still testing them to narrow down which products may be contaminated. However, Diamond decided on a broad recall of all pet food made at that plant from September 1 through December 10 while it awaits further test results. While there have been "some deaths," Brinkmann could not quantify how many animals were affected. Calls about sick animals came initially from New York and North Carolina, but the company has received inquiries from customers in several other states since the recall was announced, he said. Clinical signs of aflatoxin poisoning include loss of appetite, jaundice, severe and persistent vomiting and fever.