The Kakhovka hydroelectric dam in southern Ukraine was partially destroyed on Tuesday, with Moscow and Kyiv accusing each other of being responsible.
News of rising water levels were noted in several areas near the dam as expectations built over Ukraine's long-awaited offensive against Russian forces.
"Kakhovka hydroelectric plant. Another war crime committed by Russian terrorists. The president has convened the National Security Council," the Ukrainian president's chief of staff, Andriy Yermak, wrote on Telegram.
The Kakhovka dam, seized at the start of the Russian offensive in Ukraine, notably supplies water to the Crimean peninsula, annexed by Moscow in 2014.
"Multiple strikes targeted the Kakhovka dam" overnight in Nova Kakhovka, the head of the city's Moscow-backed administration, Vladimir Leontiev said, claiming they had destroyed the dam's gate valves and caused an "uncontrollable" flow of water.
Built on the Dnipro River in 1956, during the Soviet era, the structure is partly made of concrete and partly of earth. It is one of the largest pieces of infrastructure of its kind in Ukraine.