Russia said on Wednesday that Japan had failed to provide full information on the treated radioactive water being discharged from the wrecked Fukushima No. 1 nuclear power plant, despite repeated requests from both Moscow and Beijing.
Japan started releasing water from the plant into the Pacific Ocean in August, and was heavily criticized by China, which immediately banned all seafood imports from Japan.
"We and China have repeatedly urged the Japanese side to show transparency and provide all interested states with full access to all information about the discharge of water from the Fukushima-1 nuclear power plant," Russian Foreign Ministry spokeswoman Maria Zakharova said.
"Japan has not done this," Zakharova said. "Japan has failed to properly respond to these issues and to guarantee the absence of a threat, including a long-term one."
A massive earthquake and tsunami in 2011 triggered a nuclear meltdown at the Fukushima No. 1 plant — the world's worst nuclear disaster since Chernobyl 25 years earlier, in what was then Soviet Ukraine.
Japan says the release is safe, noting that the International Atomic Energy Agency (IAEA) has concluded that the impact on people and the environment is "negligible."
Russia is considering joining China in banning Japanese seafood imports, a Russian regulator said last month.
Zakharova said most of Russia's concerns would be "immediately removed if Tokyo stopped the process of draining its waste into the world's ocean," adding that China had expressed the same view.