WASHINGTON (Reuters) - The United States issued an import alert for Chinese-made food products on Thursday, calling for foods to be stopped at the border unless importers can certify they are either free of dairy or free of melamine.

Two top U.S. health officials announced they will go to China next week to open food inspection offices and talk about food safety after a series of health scares from Chinese-made food products.

Health and Human Services Secretary Mike Leavitt and Food and Drug Administration Commissioner Dr. Andrew von Eschenbach will also open new FDA offices in Beijing, Guangzhou and Shanghai.

At least four Chinese children have died and tens of thousands were made ill this year from drinking milk powder adulterated with melamine, a chemical used to cheat nutrition tests. Many countries have begun checking Chinese exports of milk and egg products.

Last year, melamine-tainted pet food ingredients from China were blamed for the deaths of dogs and cats in the United States.

The FDA said the ban widens earlier health alerts about Chinese products. The burden will be on the importer to certify food does not contain dairy products, or is melamine-free.

"No adverse health effects have been reported in the United States from contamination with melamine of dairy products or dairy-containing products," the FDA said in a statement

Melamine, used in making plastic chairs among other things, has been added to food to simulate higher protein content and has since been found in dairy products, eggs and animal feed, prompting recalls of Chinese-made products around the world.

Two brands of Chinese toothpaste were banned in the Dominican Republic in May 2007 because of fears that they contain the lethal chemical diethylene glycol, held responsible for mass poisoning deaths in Panama in 2006.

In February, Chinese-made frozen dumplings contaminated with pesticide made 10 people in Japan sick.

Chinese-made heparin, a blood thinner, was blamed for the deaths of 81 U.S. patients.

And Chinese toys were recalled last year because of lead paint and tiny magnets that could be swallowed.

HHS said the Leavitt and von Eschenbach visit would help to address some of these issues. "In addition, during this trip, the Secretary and the Commissioner will open FDA's new offices in three cities in China," HHS said.

The FDA offices are meant to help start inspections of Chinese products before they are exported to the United States.