An alliance of South Korean anti-nuclear and environmental groups called Japan's decision to release radioactive water from the Fukushima nuclear plant an act of "nuclear terror," urging Tokyo to immediately withdraw its plan.

Thirty-one groups on Tuesday warned that, despite Tokyo claiming it will dilute radioactive levels to meet international standards, the release will have catastrophic consequences on humans and the marine ecosystem.

Greenpeace International Executive Director Jennifer Morgan expressed outrage that Japan and the Tokyo Electric Power Company(TEPCO) think they can justify the deliberate dumping of nuclear waste into the Pacific Ocean.

Morgan added that it is a violation of Japan's legal obligations under the United Nations Convention on the Law of the Sea(UNCLOS).

Greenpeace also urged the South Korean government to take the case to the International Tribunal for the Law of the Sea and to ramp up pressure against Tokyo in solidarity with international civic groups.