Tokyo (CNN) -- Short-term exposure to food contaminated by radiation from Japan's damaged Fukushima Daiichi nuclear plant poses no immediate health risk, a spokesman for the World Health Organization said Monday.
The United Nations organization initially said the food safety situation was "more serious" than originally thought. But spokesman Peter Cordingley said Monday that the assessment was based not on the levels of contamination but on the fact that radioactivity was found in food beyond the 30-kilometer (18.6-mile) evacuation zone.
"It's new and something we're watching," Cordingley said.
On Monday, authorities in the village of Iitake urged residents to avoid drinking tap water that tests showed contained more than three times the maximum standard of radioactive iodine. The day before, a government ban on the sale of raw milk from Fukushima Prefecture and spinach from neighboring Ibaraki Prefecture became public.
The government has also banned sales of spinach and milk from parts of Gunma and Tochigi Prefectures, according to the prime minister's office.
Japanese officials reported levels of radioactive iodine in milk from four locations in Fukushima that ranged from about 20% over the acceptable limit to more than 17 times that limit. Testing at one location also found levels of cesium about 5% over the acceptable limit, the health ministry reported Sunday.
In Ibaraki, a major center of vegetable production, tests at 10 locations found iodine levels in spinach that ranged from 5% over acceptable limits to more than 27 times that ceiling. At seven sites, levels of cesium grew from just above 4% to nearly four times the limit.
Japanese Chief Cabinet Secretary Yukio Edano stressed that he believed the levels of radiation in food -- while above the legal standards -- do not pose any immediate health risk, saying they were mostly dangerous only if consumed repeatedly over one's lifetime.
The government will provide compensation for revenue lost by the restrictions, Edano said.
The water tested in Iitake contained 965 becquerels per kilogram, versus the 300 becquerels limit, Japan's health ministry said in a statement. A becquerel is the International System unit of radioactivity, equal to one nuclear decay or other nuclear transformation per second.
Although drinking the water in Iitake was discouraged, Edano said there is no problem in using this water for nondrinking purposes, such as bathing. He added, "This level is reportedly going down now."
Water in other jurisdictions showed lesser signs of contamination, although far below levels of concern under Japanese law, according to the International Atomic Energy Agency website. The U.N. agency said it had received reports from Japan's government that six out of 46 samples tested positive for the iodine-131 radioactive isotope.
Iodine and cesium isotopes are byproducts of nuclear fission in reactors such as the ones damaged in the March 11 earthquake and tsunami that devastated northern Honshu, Japan's main island. Although iodine-131 has a radioactive half-life of eight days, cesium-137's half-life is about 30 years.
High levels of radioactive substances have also been found in seawater near the plant, Tokyo Electric Power Co., the plant operator, said Tuesday, adding that the results do not represent a threat to human health.
Seawater radiation monitoring detected levels of iodine-131 that were 126.7 times higher than government-set standards, the electric company said on its website. Its monitors detected caesium-134, which has a half-life of about two years, about 24.8 times higher than the government standards. Cesium-137 was found to be 16.5 times higher than the standard.
The electric company detected these levels in seawater 100 meters (328 feet) south of the nuclear power plant Monday afternoon. Radioactive particles disperse in the ocean, and the farther away from the shore a sample is taken, the less concentrated the contamination should be.
Because of the huge amount of dilution that happens in the ocean, there's not much chance of deep-water fish being tainted, said Murray McBride, a professor at Cornell University, who studies crop and soil sciences.
The electric company is scheduled to resample seawater near the plant Tuesday.
Besides causing devastation throughout northeast Japan, the 9.0-magnitude earthquake and subsequent tsunami on March 11 seriously damaged several reactors at the Fukushima Daiichi nuclear plant, leading to the release of an unspecified amount of radioactive material into the atmosphere.
Cordingley said Japan is taking a "very precautionary" approach with its actions. Whereas fears initially were for produce within 30 kilometers of the plant, cows (and the milk they produce) outside that radius and spinach from as far as 120 kilometers was being affected.
"We have seen Japanese people in grocery stores paying close attention to where their produce is coming from, and we think this is a wise practice," he said.
Tokyo resident Phil Knall said he expects the questions about the food supply to linger.
"It doesn't look like a short-term issue," he said. "I'm definitely concerned about the food that is going to be shipped out from now. I'm definitely thinking about it."
The decision to prohibit produce sales is another potentially devastating blow to a part of northeast Japan hit by the earthquake, tsunami and other potential fallout from the Fukushima plant.
Fukushima, northeast of Tokyo, has Japan's fourth-largest amount of farmland and ranks among its top producer of fruits, vegetables and rice. Ibaraki, south of Fukushima, supplies Tokyo with a significant amount of fruits and vegetables and is Japan's third-largest pork producer.
For radiation to be an issue for rice, the contamination would have to be more severe and prolonged that what has been seen so far, said McBride, the Cornell University professor.
Amidst more severe levels of radiation, radioactive particles that fall from the air could contaminate the soil, and the plant could take them in. Soil contamination was a huge issue around Chernobyl, but the radiation issue at Fukushima Daiichi isn't anywhere near that situation, he said.
"We're not at that stage; that's the scenario you have to consider if contamination gets severe enough," McBride said.
After the 1986 nuclear plant disaster in Chernobyl, then a part of the Soviet Union, tons of food had to be destroyed when radioactive debris fell on crops in large swaths of Eastern Europe and Scandinavia.
Hygiene expert Satoshi Takaya, who helped Japanese scientists prevent contaminated food from entering the country at that time, said the current situation is no Chernobyl -- but he said the current crisis is sure to affect Japanese farmers.
That means threatening the livelihood of people like Ukia Uchida, an 82-year-old woman whose family has farmed a plot in Shibayama for generations.
"Up until now, I thought everything was fine here," Uchida said. "But to hear that some radiation has been found here is pretty upsetting."
CNN's Jo Kent, Catherine E. Shoichet, Steven Jiang, Martin Savidge, Paul Ferguson, Thom Patterson, Matt Smith and Elizabeth Landau contributed to this report