abnormal amount of a radioactive material was detected in spinach grown about 110 kilometers (about 70 miles) northeast of Tokyo.

Raising concerns over possible contamination from the stricken Fukushima Daiichi nuclear plant, Japan's health ministry said Saturday that an abnormal amount of a radioactive material was detected in spinach grown about 110 kilometers (about 70 miles) northeast of Tokyo.

The ministry also said that an abnormal amount of the material, called iodine-131, was detected in milk from a dairy farm about 50 kilometers away from the plant.

"This is the first time ever that an abnormal amount of radioactive material has been detected in food in Japan," said ministry official Ryusuke Hagiwara.

Chief Cabinet Secretary Yukio Edano said that the amounts detected in the milk and spinach would not immediately affect human health. Even so, concerns over possible food contamination mark a serious setback in Japan's attempts to contain its worst-ever nuclear accident as it threatens to widen the economic impact of the disaster to Japan's declining farming industry.

The Department of Homeland Security checks inbound goods at U.S. ports for radioactive material.

Japan has limited food exports to the U.S. and the export of one group of products - high-quality beef - was halted in April, 2010 after an outbreak of foot-and-mouth disease in Japan. Currently the U.S. doesn't allow Japan to import beef, pork poultry or processed egg products. Other products, including those containing small amounts of meat, poultry and egg products, are exported to the U.S. under Food and Drug Administration jurisdiction, an Agriculture Department spokesman said.

Also Saturday, Japan's science ministry said that small amounts of a radioactive substance not usually present have been detected in tap water in Tokyo and five nearby prefectures, but it said the amounts are too small to pose a threat to human health. The ministry started monitoring tap water for radioactive material Saturday, and will continue to check it every day.

In raw milk samples collected from a farm in the town of Kawamata in Fukushima prefecture, up to 1,510 becquerel per kilogram of iodine-131 were detected, about five times the limit of 300 becquerel per kilogram set by law.