Japan expanded its ban on cattle-shipments to a third area Monday, as nuclear contamination threatened more of the country’s beef production.

Chief Cabinet Secretary Yukio Edano told reporters the government has extended the ban to Iwate prefecture, the nation’s fifth-largest beef producer, after banning shipments last month from Miyagi and nearby Fukushima prefectures.

Radiation from the damaged Fukushima nuclear plant poses a growing threat to Japan’s food supply, as unsafe levels of cesium are found in animal feed, vegetables and beef on supermarket shelves.