Seoul's foreign ministry summoned Japanese ambassador Koichi Aiboshi on Tuesday to protest Japan's decision to dump radioactive water from the Fukushima nuclear power plant into the ocean.
South Korea's Second Vice Foreign Minister Choi Jong-moon relayed the South Korean people's opposition to the plan, and "deep concerns" over possible threats to human health and the environment.
Choi urged Japan to provide transparent information, and to stick to internationally acceptable standards and objective verification.
Earlier in the day, South Korea had vowed to deliver its concerns to the International Atomic Energy Agency.
"We plan to relay our people's concerns and opposition to this plan to the Japanese government. Japan's decision is absolutely unacceptable. The decision was made unilaterally without enough consultations with its closest neighbor, South Korea."
Seoul will thoroughly monitor for any inflow of radioactive material and tighten its screening of food products from Japan.
China also strongly condemned Japan's decision, calling it "irresponsible and unilateral."
Saying releasing radioactive water into the ocean will cause serious damage to Japan's neighbors, Tokyo should not do so until they reach an agreement with its neighboring countries or the IAEA.
The U.S., however, called the decision "in accordance with globally accepted nuclear safety standards," adding that it looks forward to Japan's continued coordination on the issue.
In a press statement, the State Department said Tokyo had taken measures in close coordination with the IAEA.
The Fukushima nuclear power plant was rendered unusable by the powerful earthquake and tsunami in 2011, and the facility is running out of space to store more than 1.2 million tons of contaminated water.
The discharge is likely to start in 2023.
Yoon Jung-min, Arirang News.