The international nuclear watchdog warned Japan in 2008 that powerful earthquakes could be too strong for their nuclear reactors, according to a U.S. diplomatic cable released by WikiLeaks Tuesday night.

During a December 2008 G8 Nuclear Safety and Security Group (NSSG) meeting in Tokyo, an official from the International Atomic Energy Agency (IAEA) said that saftey plans were out of date and that earthquakes could be a "serious problem" for aging Japanese nuclear reactors.

"On earthquakes and nuclear safety, the IAEA presenter noted the Agency has officials in Japan to learn from Japan's recent experience dealing with earthquakes and described several areas of IAEA focus," the leaked document said.

"First, he explained that safety guides for seismic safety have only been revised three times in the last 35 years and that the IAEA is now reexamining them."

"Also, the presenter noted recent earthquakes in some cases have exceeded the design basis for some nuclear plants, and that this a serious problem that is now driving seismic safety work," the cable added.

"The cables also disclose how the Japanese government opposed a court order to shut down another nuclear power plant in western Japan because of concerns it could not withstand powerful earthquakes," according the the Daily Telegraph.

The court ruled that residents could be exposed to radiation in the case of a powerful earthquake. The plant in question was only designed to handle a "6.5 magnitude" earthquake.

"Japan's Nuclear and Industrial Safety Agency believes the reactor is safe and that all safety analyses were appropriately conducted," the cable said.

A cable released Tuesday night revealed that Taro Kono, a liberal Democrat and member of Japan's DIET, or parliament, allegedly told American diplomats about coverups carried out in Japan's nuclear plants.

"Kono claimed Japanese electric companies are hiding the costs and safety problems associated with nuclear energy, while successfully selling the idea of reprocessing to the Japanese public as 'recycling uranium.'"

The cable added: "He also accused [Japan's Ministry of Economy, Trade, and Industry (METI)] of covering up nuclear accidents, and obscuring the true costs and problems associated with the nuclear industry."

Japan has 54 nuclear reactors; 11 were taken offline following last week's 9.0 earthquake and tsunami that swept across the norther portion of the country.

-- with earlier reporting by Stephen C. Webster