The world's nuclear watchdog has urged Japan to explain more clearly what is happening at Fukushima and avoid sending "confusing messages'' about the disaster, the country's atomic regulator says.
The International Atomic Energy Agency questioned why the leak last week of 300 tonnes of highly radioactive water merited a rating on its International Nuclear Event Scale (INES), when no other incident since the March 2011 meltdowns had.
The watchdog's criticisms came as Japanese Prime Minister Shinzo Abe said his government would take charge of the clean-up operation following withering criticism of the plant operator's ability to get the job done.
Local regulators yesterday rubber-stamped their earlier assessment of the huge spill, in which one of around 1000 tanks at the site was found to be holed, as being INES Level 3.
That made it the single most serious incident since three reactors went into meltdown after being swamped by the earthquake-sparked tsunami.
The initial catastrophe, which spewed radiation over the countryside and sent tens of thousands of people fleeing, was rated Level 7, the same as the 1986 Chernobyl disaster.
Last week's spillage was "the most recent of a number of events that involved leakage of contaminated water'', the IAEA said in a document submitted to Japan's Nuclear Regulatory Authority.
"Previous similar events were not rated on the INES scale. The Japanese Authorities may wish to prepare an explanation for the media and the public on why they want to rate this event, while previous similar events have not been rated.''
Fukushima operator Tokyo Electric Power (TEPCO) is struggling to deal with the vast - and growing - volume of now polluted water it has used to cool the broken reactors.
It said last week that some of the 300 tonnes that leaked from the tank could have made its way through drainage systems into the Pacific Ocean.
That came on top of the admission that groundwater contaminated by water from the plant was flowing into the sea at a rate of 300 tonnes a day, taking its low-level radioactive load with it.