Tokyo Electric Power Co. said Friday it has begun injecting freshwater into the No. 1 and No. 3 reactor cores at the crisis-hit Fukushima Daiichi nuclear plant to enhance cooling efficiency, but highly radioactive water was later found leaking near all four troubled reactor units at the plant.

A day after three workers were exposed to water containing radioactive materials 10,000 times the normal level at the turbine building connected to the No. 3 reactor building, a water pool with similarly highly concentrated radioactive materials was found in the No. 1 reactor's turbine building, causing some restoration work to be suspended, it said.

Pools of water that may have seeped from either the reactor cores or spent fuel pools were also found in the turbine buildings of the No. 2 and No. 4 reactors, measuring up to 1 meter and 80 centimeters deep, respectively, while those near the No. 1 and No. 3 reactors were up to 40 cm and 1.5 meters deep.

The latest development in Japan's worst nuclear crisis raises the risk of more workers being exposed to radioactive substances, hindering their efforts to restore the plant's crippled cooling functions that are key to overcoming the crisis.