WASHINGTON -- The Food and Drug Administration has restricted the entry of all food products from China containing milk after inspectors found evidence of melamine contamination, which has sickened tens of thousands of Chinese infants and caused at least four deaths.

The FDA directive requires importers to prove their food and drink shipments don't contain the industrial chemical melamine before they can be released to U.S. markets. The order may affect a big chunk of China's $3.8 billion in annual food and beverage exports...