Americans have no reason to fear any health effects from the nuclear power plant accident in Japan, should take no protective measures and should avoid no foods, federal health officials said Tuesday.

In a display of solidarity, eight representatives of the Centers for Disease Control and Prevention, the Food and Drug Administration and the Environmental Protection Agency delivered the slightly complicated message that while no amount of radiation is absolutely safe, the amount released by the damaged reactors is so small that the chance it will cause disease is nil.

“Due to distance and dispersion to the U.S., we do not expect levels [of radiactivity] to reach us that would cause a public health effect,” Thomas Frieden, director of the CDC, told reporters in a telephone news conference.

He said, however, that radioactive iodine has been detected in the United States and “we would be surprised if we did not detect very low levels” of radioactive cesium and strontium — two other released contaminants — in coming days. The anticipated detections say more about the sensitivity of the machinery than about the levels found, he said.

“It’s not as if there is none in the environment before this. Now, extraordinarily small amounts are being added,” Frieden said.

On Tuesday, Japan placed radiation safety standards on fish for the first time. According to press reports, samples of a fish called a sand lance caught in Japanese waters last week had elevated levels of iodine-131, which loses half its radioactivity every eight days.

The CDC director said the agency has heard that numerous poison control centers around the country have gotten calls from people who took potassium iodide, a pill that blocks the thyroid gland from absorbing radioactive iodine. He did not provide details about the calls but said: “I want to be unambiguous. There is no reason for anyone in the United States to take potassium iodide at the present time.”

There are no other medicines that protect against radiation exposure, and the public should be wary of substances advertised as able to do so, the experts said.

“There’s absolutely nothing approved that might be called a silver bullet,” said Patricia Hansen, an FDA scientist.

William Jones of the agency’s office of food safety said there “isn’t any concern of contamination of seafood” consumed in the United States because of the “extreme dilution factor” of the radioactive water currently being released into the ocean from the Japanese plant.

All shipping containers entering the United States, including ones containing food products, are screened for radioactivity, said Siobhan DeLancey, an FDA spokeswoman. If elevated levels are found, the contents can be sampled and further checked by hand.

The agency has banned imports of Japanese leafy vegetables and some head vegetables (such as cauliflower) from Fukushima prefecture, where the plant is located; milk from two prefectures; and specified fresh food from four prefectures. It is in the process of testing seven food imports that fall into the broad categories of artificial flavorings, dry tea and starches, DeLancey said.