The U.S. Food and Drug Administration announced on Tuesday that it would bar imports of some dairy products and fresh produce from the area around Japan’s damaged Fukushima Daiichi nuclear plant.

In a guidance issued to field personnel, FDA said shipments of spinach, milk and a leafy green called kakina from the prefectures of Fukushima, Gunma, Ibaraki and Tochigi could be turned away without inspection.

A day earlier, the Japanese government halted distribution of those products to both domestic or export markets, after tests revealed the presence of radioactive iodine at five times the acceptable levels.

“FDA recognizes that the government of Japan is taking steps to address this issue and FDA will continue to provide support to their efforts,” the guidance stated, meaning this is an extra precaution to keep radiation-tainted foods out of the U.S. food supply.

Prior to this, FDA had only said it was closely monitoring those foods.

All other imported food products produced or manufactured in the four affected prefectures will be diverted for testing, the agency said. Food imports from other parts of Japan will be tested as resources allow.

Less than 4 percent of U.S. food imports come from Japan, according to FDA, and the most common are seafood, snack foods, and processed fruits and vegetables. Officials insist there is very little risk from the radiation. Japan’s Chief Cabinet Secretary Yukio Edano has said consuming the affected milk and spinach every day for a year  — or eating about two pounds of contaminated spinach — would expose someone to about the same radiation as one CT scan.

U.S. Rep. Rosa DeLauro, D-CT, ranking member on the House subcommittee that controls FDA’s budget, asked agency officials Tuesday how they could say with certainty that Japan’s nuclear emergency posed no rise to the U.S. food supply.

She urged them to “act swiftly to set aside for testing all food imports from Japan.”

In a letter to Commissioner Margaret Hamburg, DeLauro’s quizzed the agency on several counts, including what specific steps were being taken to scrutinize Japanese food products, whether import inspectors were conducting radiological testing and how FDA is coordinating with the Department of Homeland Security on the issue.