WASHINGTON – The U.S. Food and Drug Administration has expanded its checks for possible melamine-contaminated food products from China to include candy and other items, a spokeswoman said Tuesday.

Chinese authorities are trying to roll back exports of milk products contaminated with the industrial chemical melamine.

Infant formula tainted with the chemical has put nearly 13,000 Chinese babies into the hospital with painful kidney stones. Four have died.

“The FDA has expanded its Asian market sampling and import surveillance assignments to include additional products such as dairy-based candies, dairy-based desserts and other such products reported to the agency as having been tested in other countries and found positive for melamine or its analogs,” FDA spokeswoman Stephanie Kwisnek said by e-mail.

“We are testing and we continue to test the products. So far, the FDA has not found any positive samples in the products it has tested.”

Melamine, which can be used to cheat quality checks by mimicking food protein, has been found in candy, buns and carton milk sold to other countries and regions, unleashing fear in markets already shaken by a string of “made-in-China” scandals last year.

China has the world's third-biggest dairy sector by volume, after India and the United States, the Chinese dairy products industry association recently estimated.

Japan, Brunei, Singapore, Malaysia, Hong Kong and Taiwan have already banned Chinese milk products.

The FDA says is has contacted the companies that make infant formula for distribution in the United States and been assured that none import formula or source materials from China.

Inspectors have also visited Chinese markets and stores to look for imported Chinese infant formula.

“Additionally, FDA is sampling and testing milk and milk-derived ingredients and finished food products that could contain these ingredients from Chinese sources. Milk-derived ingredients include whole milk powder, nonfat milk powder, whey powder, lactose powder and casein,” the agency said in a statement last week.

(Reporting by Lisa Richwine; Writing by Maggie Fox, Editing by Will Dunham)