A power cut that prompted renewed fears of a meltdown at the crippled Fukushima nuclear power plant has been blamed on a hungry rat.

The body of the dead rat was found scorched and close to a makeshift electricity switchboard, suggesting the animal caused the 30-hour black-out at Fukushima by chewing though wires. The loss of power at the nuclear plant, which was knocked out by the Japanese tsunami in 2011, shut down cooling systems used for some of the plants reactors.

Water in three spent fuel ponds began heating up after the power cut on Monday.

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Masayuki Ono, of the Tokyo Electric Power Co (Tepco), which operated the plant before the devastating tsunami, said, "It will take several days for the temperatures to get back to normal." An investigation into the power failure is underway, with the dead rat now regarded as a likely, if unconfirmed culprit. Power was partially restored to the cooling units on Tuesday. The last one was reconnected by early yesterday.