A panel investigating the nuclear accident at Japan's Fukushima plant that followed the tsunami in March has found top-level failures in preparation and communication.
More than 20,000 people were killed when an earthquake and tsunami struck on 11 March, and tens of thousands had to be evacuated as radiation leaked from the badly damaged six-reactor nuclear plant.
The government-appointed panel said plant operator Tokyo Electric Power (Tepco) and regulators failed to sufficiently anticipate a massive tsunami and the devastating impact likely to result.
Regulators did not require Tepco to undertake measures such as additional construction after they received results of simulation tests on the impact of tsunamis.
The interim report noted that Tepco did not have enough expertise on the ground after the disaster struck and made mistakes, such as misunderstanding the functioning status of a reactor's cooling system.
The investigating panel also said the government was unable to cope with the scale of the incident.
The report says officials were vague and evasive, and delayed the release of crucial information about radiation leaks.
Last week, the authorities declared the plant had been stabilised, but said it would take decades to dismantle it completely.
The 12-member panel will release a final report next summer.