Ukrainian President Volodymyr Zelenskyy has called the collapse of the Kakhovka dam in southern Ukraine an act of “mass environmental destruction” and said the attack on such critical infrastructure would not alter Ukraine’s plans to retake territory from occupying Russian forces.

Describing the explosion that destroyed the dam as a deliberate and chaotic act by Russia, Zelenskyy said on Tuesday that the dam was blown up in a bid to “use the flood as a weapon” to hamper Ukrainian forces.

In his nightly address to the nation, Zelenskyy said Moscow was resigned to losing control of Russian-annexed Crimea and, therefore, had destroyed the region’s water supply.

“The fact that Russia deliberately destroyed the Kakhovka reservoir, which is critically important, in particular, for providing water to Crimea, indicates that the Russian occupiers have already realised that they will have to flee Crimea as well,” he said.

“We will still liberate all our land,” Zelenskyy said, adding that the blowing up of the dam would not avert a Russian defeat but would add to the post-war reparation costs that Moscow will have to pay to Ukraine one day.

The Kremlin blamed Ukraine for the dam’s collapse on Tuesday, saying Kyiv had destroyed the site to distract from the faltering launch of its counteroffensive that Moscow had already blunted.

Russian Defence Minister Sergei Shoigu said his forces had thwarted the first three days of Ukraine’s counteroffensive in battles that had left thousands of Ukrainian soldiers dead or wounded. The decision to destroy the dam was to slow the attacking Russian forces, he said.

Neither Moscow nor Kyiv provided evidence for their claims regarding the dam’s destruction.

The dam’s collapse presents a new humanitarian disaster in the centre of a war zone and as Ukraine prepares for its long-awaited counteroffensive.

‘Grave and far-reaching consequences’ Al Jazeera’s Charles Stratford, reporting from the dam’s reservoir in Ukraine’s Zaporizhia region, said that before its destruction, the dam had provided electricity and drinking water for hundreds of thousands of people in Ukraine.

“The locals that we’ve spoken to here say … that the water level today has dropped anywhere between a metre and two metres, and we expect in the coming hours and days for the level to continue dropping and on that basis, one can only imagine the kind of devastating effect that it is having on affected areas south of the dam,” Stratford said.

Ihor Syrota, head of Ukraine’s hydroelectric power authority, told the US-funded radio station Donbas Realii that flooding had caused waters to rise by 3.5 meters (11.5 feet) and that Ukrainian officials believe the flood waters would crest on Wednesday, then levels would begin to fall within three to four days.

The flooding has already submerged villages and towns around the city of Kherson and Russian officials warned that the main canal supplying water to the Russian-annexed Crimea peninsula is receiving drastically less water.

Ukrainian authorities said 17 000 people were being evacuated from Ukrainian-held territory and a total of 24 villages had been flooded. “Over 40 000 people are in danger of being flooded,” Ukraine’s Prosecutor General Andriy Kostin said, adding that 25 000 more people should be evacuated in the most critical areas at risk on the Russian-occupied side of the Dnipro River.

Vladimir Leontyev, the Moscow-installed mayor of Nova Kakhovka where the dam is located, said the city was underwater and hundreds of people had been evacuated.

The United Nations said at least 16 000 people have already lost their homes and that efforts were under way to provide clean water, money, and legal and emotional support to those affected.

People on the Ukrainian-controlled side of the river were being evacuated by ferries to cities including Mykolaiv and Odesa to the west.

UN Undersecretary-General for Humanitarian Affairs Martin Griffiths told the Security Council on Tuesday that the full “magnitude of the catastrophe” will only become fully realised in the coming days.

"The damage caused by the Kakhovka dam destruction in #Ukraine means that life will become intolerably harder for those already suffering from the conflict. Our urgent humanitarian task is to continue to help them to survive, be safe and get a future," said Griffiths.

“But it is already clear that it will have grave and far-reaching consequences for thousands of people in southern Ukraine – on both sides of the front line – through the loss of homes, food, safe water and livelihoods,” Griffiths added.

Russia and Ukraine traded blame for the disaster at an emergency meeting of the UN Security Council on Tuesday.

James Bays, Al Jazeera’s diplomatic editor reporting from the UN’s headquarters in New York, said the Russian and Ukrainian ambassadors at the council meeting gave “completely different accounts of what’s happened” to the dam.

The Russian ambassador made the point that there had been previous threats to the dam by Ukraine, Bays said, and Ukraine made the point that the dam was situated in territory controlled by Russian forces and that only mining the dam could have destroyed it, not an attack from afar.

“Those are the clear positions of the two sides and really what you need is someone to properly investigate which of these two completely different stories is true.

I don’t think that is very likely to happen anytime soon,” Bays said, noting that the dam remains a military front line.

Ukraine’s interior minister said on Tuesday that Russia was shelling areas from where people were being evacuated from the dam’s flood waters and that two police officers had been wounded.

Ben Barry, a senior fellow at the International Institute for Strategic Studies, said flooding from the dam would be to Moscow’s advantage in the short term.

“Bearing in mind Russia is on the strategic defensive and Ukraine on the strategic offensive, in the short term it’s an advantage to Russia, definitely,” Barry said. “It’ll help the Russians until the water subsides because it makes it more difficult for Ukraine to do assault river crossings,” he said.

Flood water inundating the region will also prevent the use of heavy weaponry such as tanks for at least a month, said Maciej Matysiak, a security expert at the Stratpoints Foundation and ex-deputy chief of Polish military counter-intelligence.

“(This) creates a very good defending position for Russians who expect Ukrainian offensive activity,” Matysiak said.