The March 2011 accident "counld not be regarded as a natural disaster," the Diet's Fukushima Nuclear Accident Independent Investigation Commission said. "It was a profoundly manmade disaster - that could and should have been foreseen and prevented."

The panel, established in May 2011, said the government and the plant's operator, Tokyo Electric Power (TEPCO), failed to provide adequate prevention and "lacked a sense of responsibility to protect people's lives."

Some of the plant's reactors melted down after a tsunami and 9.0-magnitude earthquake wrecked its cooling systems.

Tens of thousands of people were evacuated from a no-go zone around the stricken plant.

Numerous errors and negligence left the plant in "a vulnerable condition with no guarantee it could withstand earthquakes and tsunamis," the panel's 600-page report said.