Explosions at the Kakhovka dam near Kherson, southern Ukraine unleashed floodwaters on Tuesday, as both Moscow and Kyiv accused each other of destruction.
Ukrainian President Volodymyr Zelenskyy said on Twitter that the dam’s destruction "confirms for the whole world that they (Russian forces) must be expelled from every corner of Ukrainian land."
Later, in a video address to the Bucharest Nine Summit in Romania, Zelenskyy said that it is "physically impossible" to blow up the dam from the outside or by shelling, claiming that it was mined by Russia.
"And this once again demonstrates the cynicism with which Russia treats the people whose land it has captured, and what Russia actually brings to Europe and the world," Zelenskyy added, calling the dam's destruction "the largest man-made environmental disaster in Europe in decades."
Zelenskyy also convened an emergency meeting of the country’s National Security and Defense Council (NSDC), after which its head Oleksiy Danilov said on Twitter that the dam’s destruction marked "a fundamentally new stage of Russian aggression."
The vast dam, 30 meters (98 feet) tall and 3.2 kilometers (2 miles) long, was built in 1956 on the Dnieper River as part of the Kakhovka Hydroelectric Power Plant. It also holds a reservoir with a capacity of 18 cubic kilometers (4.3 cubic miles).
But Russia strongly rejected the accusations, claiming the dam’s destruction was a "deliberate" act of sabotage by Kyiv.
The attack was carried out by Kyiv, and it should bear full responsibility for the consequences, Kremlin spokesman Dmitry Peskov told a press briefing in Moscow.
"The president has received reports from the Defense Ministry and other agencies about what is happening around the Kakhovka HPP (hydroelectric power station) … we can unequivocally state that we are talking about deliberate sabotage by the Ukrainian side," he stressed.
Peskov claimed that Kyiv carried out the attack due to a failure of its much-anticipated counteroffensive, which he said is "choking."
One of Ukraine's goals in targeting the critical infrastructure was to deprive Crimea – now controlled by Russian forces – of water, which is supplied to the peninsula through the Kakhovka Reservoir, he added.
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Earlier, Ukrainian Foreign Minister Dmytro Kuleba called the incident "probably Europe’s largest technological disaster in decades," which puts "thousands of civilians at risk."
The head of Ukraine's southern command Vladislav Nazarov said the dam is partially breached and flooding is underway.
Vladimir Leontyev, head of the Russia-controlled city of Nova Kakhovka, located on the east bank of the Dnieper River, said on Telegram that overnight strikes by Ukraine's armed forces led to the destruction of valves, and thus the uncontrolled release of the water downstream.
Leontyev warned that the destruction of the dam may lead to water supply problems to Crimea, which Russia illegally annexed in 2014, as the Kakhovka Reservoir supplies water to the peninsula via the North Crimean Canal, as well as to the Zaporizhzhia Nuclear Power Plant (NPP).
The canal had been catering to 85% of Crimea's water needs until 2014, when it was shut down by Ukraine, leading to a water shortage. Its control is one of the objectives of Russia's "special military operation."
Leontyev claimed the Ukrainian army was shelling the city of Nova Kakhovka, adding that their main task is evacuating people.
The Novokakhovsk urban district may remain flooded for up to 72 hours, after which the water will recede, local authorities said.
No immediate safety risk at Zaporizhzhia NPP: IAEA
The International Atomic Energy Agency (IAEA) said on Twitter it is "aware of reports of damage" at the Kakhovka dam that helps cool Europe's largest nuclear power plant.
"The IAEA experts at the Zaporizhzhya Nuclear Power Plant are closely monitoring the situation; no immediate nuclear safety risk at plant," the agency added.
Ukrainian Prime Minister Denys Shmyhal tweeted that a possible dam break poses a threat to the south of Ukraine, urging pushing "Russia out of the Zaporizhzhia nuclear power plant."
The Russian Rosatom State Nuclear Energy Corporation said on Telegram that "at the moment there is no threat to the safety" of the plant.
Renat Karchaa, a Rosatom representative at the Zaporizhzhia plant, told Russian media that specialists at the plant are compensating for the decrease in the water level of the Kakhovka Reservoir "by other technical means," and that there is no risk to the cooling system.
European Council President Charles Michel said he was shocked by the "unprecedented" attack, saying the "destruction of civilian infrastructure clearly qualifies as a war crime" and that "we will hold Russia and its proxies accountable."
NATO chief Jens Stoltenberg said the destruction of the Kakhovka dam "puts thousands of civilians at risk and causes severe environmental damage."
"This is an outrageous act, which demonstrates once again the brutality of Russia’s war in Ukraine," he added.