New radiation threats have been discovered in Tokyo and the nearby city of Yokohama, suggesting that radiation from the crippled Fukushima nuclear plant remains a problem throughout much of Japan.

Officials in Setagaya, a residential area in Tokyo about 235 kilometers southwest of Fukushima, say radiation has been measured on a sidewalk near a school at levels higher than in some parts of the evacuation zone surrounding the Fukushima plant.

In Yokohama a radioactive material called strontium-90 has been discovered in soil samples taken from an apartment rooftop more than 240 kilometers from the plant. Strontium-90 can cause bone cancer and leukemia.

The Fukushima Daiichi plant was crippled by the March 11 earthquake and tsunami, which knocked out the plant's cooling systems and led to a meltdown of three of its reactors.