A radiation hotspot in Tokyo has been attributed to mystery bottles stored under a house rather than the Fukushima nuclear plant.
The hotspot in Setagaya, a major residential area in Tokyo about 235 km southwest of the plant, was discovered on a pavement near schools, seven months into Japan's nuclear crisis.
However officials said the high levels of radiation appeared to be coming from several bottles stored under the floor of a nearby house.
"A measuring device, when pointed at them, showed very high readings. Radiation levels were even exceeding the upper limit for the device," Setagaya Mayor Nobuto Hosaka said.
The radiation measured as much as 3.35 microsieverts per hour, higher than some areas in the evacuation zone near the Fukushima plant, the centre of the world's worst nuclear disaster since Chernobyl 25 years ago.
The earthquake-hit Fukushima Daiichi nuclear power plant has released radiation into the atmosphere that has been carried by winds, rain and snow across eastern Japan.
Officials from the Education Ministry are investigating, while public broadcaster NHK said no one had been living in the house in question.
The city of Funabashi, near Tokyo, said that a citizens' group had measured a radiation level of 5.8 microsieverts per hour at a park, but that the city's own survey showed the highest reading at the park was a quarter of that level.
Radiation levels in the 20 km radius evacuation zone around the Fukushima Daiichi plant ranged from 0.5 to 64.8 microsieverts per hour, government data showed this week.
About 80,000 residents have evacuated this zone. A microsievert quantifies the amount of radiation absorbed by human tissue.
In Yokohama, also near Tokyo, radioactive strontium-90, which can cause bone cancer and leukaemia, was detected in soil taken from an apartment rooftop, media reported.
Strontium has been detected within an 80 km zone around the Fukushima Daiichi plant, but this is the first time it has been found in an area so far away, local media added.
Radiation exposure from natural sources in a year is about 2,400 microsieverts on average, the U.N. atomic watchdog says.
Japan's education ministry has set a standard allowing up to 1 microsievert per hour of radiation in schools while aiming to bring it down to about 0.11 microsievert per hour.