It was the first time Chinese authorities officially responded to the uproar that has resulted in a ban on gluten imports from the Xuzhou Anying Biologic Technology Development Co. and a U.S. recall of nearly 100 brands of pet food.

"We are investigating this," Zeng Xing, an official with the press office of the General Administration of Quality Supervision, Inspection and Quarantine, told The Associated Press.

Zeng, whose agency monitors the export of food, animals and farm products, refused to give any details of the probe other than to confirm China is looking into the claim that the exported wheat gluten contained melamine, a chemical found in plastics and pesticides.

Xia Wenjun, another agency official, was cited by the state-run Xinhua News Agency as saying that "sampling and examination" of wheat gluten was under way nationwide.

The probe will center on melamine and agency officials will stay in touch with the U.S. Embassy in Beijing, Xia told Xinhua, adding that further measures would be taken "based on developments in the United States."

Chinese veterinarians and animal rights activists said they were not aware of any reports of deaths in the country from tainted pet food.

Product contamination is a widespread problem in China, but this is the first recent high-profile incident of a tainted food being exported. In domestic cases, such as one involving drug regulators who took bribes to approve shoddy drugs, the government has promised investigations.

According to state regulations, exported food should be inspected by Zeng's agency for poisonous substances. China's customs service is supposed to allow a product to pass only when a certificate of quality supervision is provided.

It wasn't immediately clear if those procedures were followed in the case of the wheat gluten, which is a protein-rich meat substitute developed in China and most commonly used in vegetarian and Asian cuisines.

Las Vegas-based ChemNutra Inc., which imported the gluten and sold it to companies that make pet food, said this week that Xuzhou Anying never reported the presence of melamine in the content analysis it provided. ChemNutra previously said none of the tainted material went to manufacturers of food for humans.

Mao Lijun, general manager of Xuzhou Anying, on Friday would say only that the allegations were "under investigation."

Chemical scares and mass poisonings are common in China, which has been struggling to improve a dismal food-safety record. Manufacturers often mislabel food products or add illegal substances to them. Cooks routinely disregard hygiene rules or mistakenly use industrial chemicals instead of salt and other ingredients.

Last year, seven companies were punished for using banned Sudan I dye to color egg yolks red. The industrial dye, a possible carcinogen used for leather, floor polish and other household chemicals, has been found in various consumer products sold in China, such as roasted meat, chili powder and lipstick.

In 2004, at least 12 infants died from malnutrition after drinking formula with little or no nutritional value in eastern China's Anhui province.

So far, the U.S. Food and Drug Administration has confirmed about 15 pet deaths, while anecdotal reports suggest hundreds of cats and dogs may have died of kidney failure from the tainted food.

Last week, the FDA blocked imports from Xuzhou Anying, which says it exports more than 10,000 tons of wheat gluten a year.

Only 873 tons have been linked to the contaminated pet food in America, raising the possibility that more of the bad product could still be in China or the United States. Xuzhou Anying says the U.S. is its only foreign market.

Marion Nestle, a nutrition professor at New York University, said importing the ingredients for food products from developing countries is becoming "increasingly common."

"This is what globalization is about," said Nestle, who is writing a book about pet food.

While regulators recognize that more and more food is reaching the U.S. from developing countries, Nestle said the Food and Drug Administration is not equipped to sufficiently monitor its quality.

"The FDA is an agency under siege," she said, lacking the funding and manpower to adequately screen imported food, though they are slowly being "reluctantly dragged into it, kicking and screaming."

Nestle said that she has always wondered why imported vegetables from Mexico, for example, don't make Americans sick when American tourists traveling in Mexico often get sick from vegetables they eat there. Experts have told her, she said, that Mexican vegetables slated for export to the U.S. are "produced under conditions that are identical to conditions in the U.S."

"But if you think about it for a second, you realize that the FDA isn't going off into the wild to inspect everything," Nestle said, noting that the agency is able to inspect only 2 percent of the goods that cross U.S. borders.

Neal Hooker, a professor of agricultural economics at Ohio State University, said that while the FDA cannot inspect every good that comes into the U.S., it does insist that developing countries meet higher production standards for the goods they intend to send to the U.S.

Hooker said the agency can be fairly effective, despite its infrequent product inspections, because it brings pressure to bear on the system of production and works with foreign governments to ensure compliance.

But government regulations are not the only — or even the most effective — means of enforcing high standards. Hooker said the market also offers powerful incentives.

The pet food companies who received tainted ingredients, for instance, "are going to ask for things much more rigorously than a nation can ask for. And they will get them," he said, or they will take their business elsewhere.

Similarly, he said, Mexican vegetable growers may have even higher production standards than U.S. farmers because certain hygienic practices can increase the shelf-life of food, allowing the use of slower — and cheaper — shipping methods.

AP writer Sarah DiLorenzo in New York contributed to this report.

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