New Leak Feared at Stricken Japan Nuclear Plant (Kiyoshi Takenaka and Yoko Nishikawa)

The disclosure by Tepco raises the stakes in a race to complete by next month a system to decontaminate a massive pool of radioactive water at the site that critics see as a growing risk to both the nearby Pacific and groundwater.

A magnitude 9.0 earthquake and the massive tsunami that followed killed about 24,000 people and knocked out the Fukushima plant on March 11, triggering the world's worst nuclear accident since Chernobyl.

The crisis, which has displaced some 80,000 residents from around the plant, prompted a review of Japan's energy policy and growing calls for efforts to step up health monitoring for a crisis now in its 11th week.

READ MORE: Yahoo News