VIENNA - A Chinese envoy on Monday reiterated China's firm opposition to Japan's discharge of nuclear-contaminated wastewater from the crippled Fukushima Daiichi Nuclear Power Plant into the ocean, calling for strengthening international supervision over the water release.

In disregard of the opposition from neighboring countries and concerns of the international community, Japan has so far arbitrarily discharged over 23,000 tonnes of nuclear-contaminated wastewater into the ocean, and started the fourth round of wastewater release last week, Li Song, China's permanent representative to the International Atomic Energy Agency (IAEA), told a meeting of the agency's board of governors.

Calling Japan's wastewater discharge an unprecedented move that imposes the risk of nuclear contamination on the world, Li said its unprecedented spillover influence extends far beyond Japan's territory and jurisdiction, and thus it is by no means the country's private matter.

Japan's wastewater release has severely impacted the international nuclear safety system, and by using the IAEA to endorse its discharge plan, Japan has seriously undermined the agency's credibility, Li said.

Li noted that China has firmly opposed Japan's wastewater discharge and urged Japan to stop the release.

In response to Japan's pushing ahead with the wastewater release, China took the lead in calling for strict and effective international supervision over Japan, for the benefit of the marine environment and human health, Li said, adding that it is the firm position and continuous efforts by China and other stakeholders that have driven the IAEA Secretariat to make international monitoring arrangements for Japan's nuclear-contaminated wastewater discharge.

Li said China also supports and actively participates in the IAEA Secretariat's monitoring work in Fukushima and maintains communication with Japan.

China's stance and support are important contributions to the international supervision of the discharge, he said. The substantive participation of China and other stakeholders provides an important guarantee for the international monitoring arrangements to achieve strict, independent and effective supervision, he added.

The Chinese envoy said that China, in a scientific and responsible manner, has raised doubts about Japan's wastewater discharge, such as the plan's legitimacy, safety, potential hazards including bio-concentration, the long-term reliability of Japan's wastewater purification equipment, the accuracy of wastewater data and the effectiveness of the current monitoring arrangements.

However, the long-standing dishonesty, chaotic management and weak supervision of the Tokyo Electric Power Company, the Fukushima plant's operator, have undermined the credibility of Japan's claim of the so-called "safe and reliable" wastewater discharge, Li said.

He added that recent developments, including safety concerns arising from the earthquake that struck the Noto Peninsula and the massive leakage of nuclear-contaminated wastewater from the Fukushima plant's purification equipment, have confirmed the concerns of China and the international community and demonstrated the necessity of strengthening international supervision and monitoring.

Li emphasized that wastewater discharge is not only a scientific issue but also a matter of attitude.

China urges Japan to take seriously the concerns from home and abroad and fully cooperate in establishing long-term, independent and effective international monitoring arrangements that involve the active participation of its neighbors and other stakeholders, Li said, calling on Japan to properly dispose of the Fukushima wastewater and prevent the harm to global marine environment and human health.

He said China stands ready to improve communication and cooperation with all parties, support and actively participate in the monitoring of Japan's discharge and continuously strengthen relevant international supervision, so as to restore clean and safe oceans for people around the world.