South Korean President Moon Jae-in ordered officials on Wednesday to explore filing an international court injunction against Japan over its decision to release 1.25 million tons of contaminated water from the destroyed Fukushima nuclear power plant into the Pacific Ocean.

“In an internal meeting, Moon ordered his government to ‘proactively consider’ bringing the matter to the International Tribunal for the Law of the Sea,” presidential spokesman Kang Min-seok told reporters at a press briefing on April 14.

“The [South Korean] office of the secretary for legal affairs has begun a review of various options, which include a formal request for the tribunal to take a provisional measure first, similar to a ‘court injunction,’ against Japan’s move,” Kang said.

Japan on April 13 approved plans to release over one million tons of contaminated water from Fukushima into the Pacific Ocean starting in 2023. The massive amount of water was used to cool some of the plant’s nuclear reactors after they suffered meltdowns in March 2011 during power outages caused by an earthquake and tsunami. The water has been stored in above-ground tanks at the Fukushima nuclear power plant since the disaster.

Japan’s government said Tuesday it plans to release the water over a period of ten years and will first treat the water through an advanced liquid processing system (ALPS) to remove most radioactive material.

“The [ALPS] process removes most radioactive materials including strontium and cesium but leaves behind tritium, which is related to hydrogen,” Japan’s Kyodo News reported on Tuesday.

“The tritium will be diluted to less than 1,500 becquerels per liter, one-40th of the concentration permitted under Japanese safety standards and one-seventh of the World Health Organization’s guideline for drinking water,” according to Tokyo’s stated plan.

An independent Japanese research body established in the aftermath of the 2011 Fukushima nuclear disaster called the Citizens’ Commission on Nuclear Energy (CCNE) expressed concern to Japan’s Mainichi newspaper on April 13 about the lack of a “uniform international standard on a level of tritium deemed safe for release into the environment.”

“Japan sets the level at 60,000 becquerels per liter, while the World Health Organization says the acceptable level is 10,000 becquerels per liter and the European Union 100 becquerels per liter,” CCNE member Masashi Goto told the newspaper.

“Such significant differences in the standards across countries prove that there is no scientific foundation for the safety of tritium,” Masashi said, adding “many countries have merely set standards because they needed to run nuclear power plants, which produce tritium as a byproduct.”

President Moon expressed similar concerns about the water’s lingering radioactive ingredients to Japan’s Ambassador to South Korea, Koichi Aiboshi, on April 14.

“I cannot but say that there are many concerns here about the decision as a country that is geographically closest and shares the sea with Japan,” Moon told Koichi, asking him to convey Seoul’s reservations to Tokyo.

Koichi met with Moon in Seoul on Wednesday to present the leader with his credentials, a formal protocol when a new envoy arrives in his or her host country. Koichi arrived in South Korea in February.

“It is unusual for the president to mention such a diplomatically sensitive issue while conversing with a group of foreign ambassadors,” Moon’s spokesman, Kang Min-seok, told reporters on April 14, according to Yonhap.