Ukraine's prime minister said Wednesday that the destruction of the Kakhovka dam was "one of the most significant environmental catastrophes in Europe in recent decades".
Speaking at the OECD in Paris by video link, Denys Shmyhal said "dozens of towns and villages will struggle with potable (drinking) water supply".
He added that the attack would also affect irrigation systems in southern Ukraine "leading to drought and crop failures. This strikes at the heart of global food security".
The destruction of the Kakhovka hydroelectric plant meant "at least 150 tonnes of machine oil has leaked into the (Dnipro) river with the risk of an additional 300 tonnes seeping out. This poses a threat to the unique flora and fauna."
He called it a "crime against humanity and an ecocide. Therefore Russia must face a powerful and unified response, not mere words".
Ukrainian President Volodymyr Zelensky accused Russia of detonating an "environmental bomb of mass destruction", saying authorities expected up to 80 settlements to be flooded and urging the world to "react".
Kyiv believes the destruction of the dam -- seized by Russia in the early hours of the war -- was an attempt by Moscow to hamper its long-awaited offensive.
Russia said the dam was partially destroyed by "multiple strikes" from Ukrainian forces and urged the world to condemn Kyiv's "criminal acts".