TOKYO (AP) — The chief of the International Atomic Energy Agency stressed the importance of transparency on Friday after visiting the tsunami-wrecked Fukushima nuclear power plant, where he observed preparations for the release of treated radioactive wastewater that has prompted concerns inside and outside Japan.

Rafael Grossi, the director general of IAEA, which is assisting Japan's plan to start releasing the wastewater into the sea next year, said his agency will help maintain transparency throughout the process.

Grossi is meeting with officials to discuss the plan, which has received international attention. On Thursday he visited the Fukushima Daiichi plant, where he observed its ongoing decommissioning and preparations for the wastewater discharge.

Japan’s government says disposal of the water, stored in hundreds of large tanks, is necessary for the plant's cleanup and decommissioning to move forward.

Grossi touched on lingering concerns in Japan and in neighboring countries about possible health hazards from the release of the wastewater, which includes tritium, a byproduct of nuclear power production that is inseparable from the water and a possible carcinogen at high levels.

“I proceed from the principle that every serious honest concern must be taken seriously and every effort must be made to address it,” he said. “For these countries, any countries, what they have every right to demand is that the international standards are complied with, nothing more, nothing less."

Grossi stressed that the IAEA's role is to ensure that measures taken at the plant are fully in line with international standards that have been accepted by those expressing concerns. China and South Korea have fiercely opposed the plan.

Local fishing communities say the release will hurt the reputation of their catch because the wastewater also contains other isotopes such as cesium and strontium, which will be reduced way below legal limits, but not to zero.

Japan's government has faced repeated public criticism for minimizing any risk from the wastewater. Last year, the reconstruction agency had to remove a video which portrayed tritium as a cute cartoon character swimming in a glass of water.

Japan’s nuclear regulator this week approved a plan by the plant's operator, Tokyo Electric Power Company Holdings, to release the water, saying radiation risks to the environment were minimal.

A massive earthquake and tsunami in 2011 destroyed the Fukushima plant’s cooling systems, causing three reactor cores to melt and release large amounts of radiation. Water that is being used to cool the damaged reactor cores, which remain highly radioactive, has since leaked into the reactor basements, where it is contained, collected and stored in tanks.