TOKYO (REUTERS) - The operator of the crippled Fukushima nuclear plant said on Tuesday that four tonnes of rainwater that may be contaminated leaked during a transfer of radioactive water between tank holding areas.

Tokyo Electric Power Co, or Tepco, has been trying to contain contaminated water at the Fukushima site after it found 300 tonnes of radioactive water had leaked out of one of its tanks at the plant. The Fukushima plant suffered triple nuclear meltdowns and hydrogen explosions after a March 2011 earthquake and tsunami.

A Tepco spokesman said on Tuesday that it was not immediately clear how contaminated the water was and that the utility was sampling the water to check radiation levels.