The head of the United Nations' nuclear watchdog was met with protests while visiting South Korea on Saturday in a bid to calm fears over Japan's plan to discharge treated radioactive water from its tsunami-hit Fukushima plant.

Rafael Grossi, director general of the International Atomic Energy Agency (IAEA), arrived in Seoul on Friday to meet the foreign minister and a top nuclear safety official during his three-day visit after wrapping up a trip to Japan.

Earlier in the week, the IAEA said that a two-year review showed Japan's plans for the water release would have a negligible impact on the environment.