Japan's top government spokesman on Monday blasted the operator of the stricken Fukushima Daiichi nuclear plant for giving an erroneous radiation reading, calling it "unacceptable".
On Sunday Tokyo Electric Power Co. said radiation in puddles in the turbine building of reactor two at the plant was 10 million times higher than normal, before later correcting the information to say it was 100,000 times higher.
Top government spokesman Yukio Edano said: "Considering the fact that the monitoring of radioactivity is a major condition to ensure safety, this kind of mistake is absolutely unacceptable.
"(The government) has ordered TEPCO not to repeat this again," he said.
However he added that he understood workers at the site were probably exhausted from their round-the-clock efforts to avert a nuclear disaster at the stricken plant.
The radiation level in the water puddle at reactor two soared to more than 1,000 millisieverts per hour, forcing the evacuation of workers toiling to restore its cooling systems.