The Japanese Government says there is no need to expand the evacuation zone around the Fukushima nuclear power station, despite mounting pressure to move more people away from the crippled plant.
The current evacuation zone is limited to a 20km radius around the stricken reactors, which have been in crisis since the March 11 earthquake.
Most foreign governments have told their citizens to go no closer than 80km, and Japanese opposition parties have attacked Prime Minister Naoto Kan for failing to widen the exclusion area.
Now both the UN nuclear watchdog and Japan's own nuclear safety agency say radiation 40km from the plant exceeds levels set for evacuation.
Greenpeace says radiation levels it measured independently in one village could cause long-term health effects if people were exposed to it over several days.
After a series of explosions and fires, the operators of the Fukushima facility have struggled to bring it under control.
Japanese authorities have accepted that all six reactors will have to be scrapped, but experts say that process may take decades of work.
It has also been revealed that seawater near the power station contains radioactive iodine 4,385 times the legal limit, suggesting radiation is leaking continuously from the plant into the ocean.
Radiation has already tainted Tokyo's tap water, as well as milk and produce in the region closest to the Fukushima reactors.
Recent tests have also found higher-than-normal radiation in Japanese cabbages exported to Singapore, and even in milk samples on the US west coast, though scientists say neither case is at levels harmful to human health.
The disaster has prompted Japan to draw up new rules for its nuclear power plant operators, which already supply around a third of the country's electricity. Several other countries have followed suit.
US President Barack Obama has also announced a safety review of America’s existing nuclear facilities, saying "lessons from Japan" will be used in the building of any new plants.
China, home to nearly half of the nuclear plants currently under construction, has halted approvals for any new facilities.
Nicolas Sarkozy, the first foreign leader to visit Japan since the earthquake, has also called for a meeting of G20 nations to define nuclear safety standards.