A power cut at Japan's tsunami-crippled nuclear plant this week may have been caused by a rat, according to officials.

Masayuki Ono, spokesman for Tepco (Tokyo Electric Power Company), the utility that runs the Fukushima Daiichi plant, said a 6-inch rodent was found dead near a switchboard. He said the rat might be linked to the power failure, but further investigations were needed.

Cooling systems at the plant for four storage pools for nuclear fuel were knocked out on Monday. Power was restored two days later at all nine affected facilities.

Concerns over the site of the world's worst nuclear accident since Chernobyl remain unresolved, and decommissioning the tsunami-damaged backup generators that triggered the March 2011 disaster is expected to take decades.