TOKYO - Japan's Chief Cabinet Secretary Yukio Edano slammed Tokyo Electric Power Co. (TEPCO) on Thursday, saying it was deplorable that the utility firm could allow another leak to occur from the stricken Fukushima No 1 nuclear plant.

Japan's top government spokesperson said that the highly radioactive leak that was announced by TEPCO on Wednesday and subsequently stopped, threatened not only Japan's marine environment but potentially a host of other countries' too.

"I apologize for again causing worries and troubles to local residents, those in the fishing industry and neighboring nations," Edano told a news conference

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TEPCO said that, in a case almost identical to the one last month, water was seen leaking through power cable ducts in a concrete pit near to the sea wall which serves as a water intake for the No 3 reactor.

Japan's Nuclear and Industrial Safety Agency demanded TEPCO ensure the route of the highly contaminated water was established and that the leak plugged swiftly. In addition the affects on the environment will need to be assessed the agency said.

Last month a similar situation saw water containing radioactive iodine-131 more than 10,000 times the legal concentration limit freely leaking into the Pacific Ocean from a cracked pit connected to the No 2 reactor turbine building.

The utility firm struggled to find suitable materials to stem the flow and at one point resorted to using garbage bags filled with shredded newspaper until a permanent solution was found.

On April 2 TEPCO said that samples taken from seawater near one of the reactors contained 7.5 million times the legal limit for radioactive iodine following radioactive water leaking from the stricken nuclear facility into the ocean.