Prime Minister Naoto Kan on Wednesday banned the shipment of shiitake raised outdoors in eastern Fukushima Prefecture near the crippled nuclear power plant after radioactive substances exceeding government standard were detected.

Subject to the ban are shiitake harvested outdoors on logs in the cities of Date, Soma, Minamisoma, Tamura, Iwaki, and the towns of Shinchi, Kawamata, Namie, Futaba, Okuma, Tomioka, Naraha, Hirono as well as the villages of Iitate, Katsurao and Kawauchi.

"Shiitake mushrooms subject to the shipment ban this time are those raised outdoors and those produced indoors did not exceed the standard," Chief Cabinet Secretary Yukio Edano said. "We will lift the ban when the (level of radioactive substances) stays below the standard in a stable manner."

According to government regulations, a shipment ban will not be lifted unless contamination levels of produce near the Fukushima No. 1 nuclear plant remain below legal limits in three consecutive tests.

A test Sunday found 12,000 becquerels per kg of radioactive iodine and 13,000 becquerels per kg of cesium in shiitake harvested in Iitate. The figure is well above the legal limit of 2,000 becquerels for radioactive iodine and 500 becquerels for cesium.

Shiitake in Iwaki was found to have 3,100 becquerels of radioactive iodine and 890 becquerels of cesium.