Plutonium has been found in the soil at the Fukushima nuclear power station in Japan.
The plant’s operator Tepco said traces of the radioactive matieral were found in five locations, but not at dangerous levels.
Earlier it was revealed that highly radioactive water had been detected in tunnels outside the reactors.
The Japanese government has criticised Tepco for miscalculating radiation levels at Fukushima.
The UN’s nuclear watchdog, the International Atomic Energy Authority, is to address safety concerns worldwide because of the crisis prompted by the earthquake and tsunami in Japan.
“The situation remains very serious, it continues to be very serious and the priority for now is to overcome the crisis. I propose that a high level IAEA conference on nuclear safety should take place here in Vienna before this summer”, said the IAEA’s Director-General Yukiya Amano.
The crisis continues to provoke anti-nuclear protests outside Japan. About 50 activists gathered in central Seoul to demonstrate against nuclear energy in South Korea.