Amano pledged to send a team to Japan this autumn to deal with the increasingly worrisome problem.

Meanwhile, plant operator TEPCO announced samples taken from a well near the site tested positive for the presence of radioactive substances, including strontium.

Reports produced by TEPCO admit radioactive water from leaking storage tanks has contaminated ground water and reached the sea. The level of radiation at the well was measured at 3,200 becquerels per liter.