The Khakhovka dam was blown up by Russian forces to prevent Ukrainian troops from advancing in the southern Kherson region, deputy defence minister Hanna Maliar says.
Ukraine has accused Russian forces of blowing up the dam from inside its associated hydroelectric power station. The site has been under Russian occupation since the early weeks of Russia's invasion in February last year.
Moscow has blamed the destruction of the dam on Ukraine. Each side has accused the other of shelling civilians as rescue efforts are carried out.
"The explosion of the Kakhovka hydroelectric power station was apparently carried out with the intention of preventing the Ukrainian Defence Forces from launching an offensive in the Kherson sector," Maliar said on the Telegram messaging app on Sunday.
She said the action, which unleashed a vast flood which inundated towns and villages, trapped residents and swept away entire houses, was also aimed at helping allow the deployment of Russian reserves to the Zaporizhzhia and Bakhmut areas.
Ukrainian President Volodymyr Zelenskiy said on Saturday that counteroffensive and defensive operations were taking place in Ukraine.
"Counter-offensive and defensive actions are taking place in Ukraine, but I will not say in detail what stage they are at," Zelenskiy said at a news conference with Canadian Prime Minister Justin Trudeau.
"They (the generals) are all in a positive mood. Pass that on to Putin," he said with a smile.
Russian President Vladimir Putin earlier said Ukrainian forces had made no progress.
Russia's Defence Ministry said on Saturday Ukrainian forces had in the past 24 hours made "unsuccessful" attempts to attack in the southern Donetsk and Zaporizhzhia regions - two areas subject to heavy fighting.
In his nightly video address, Zelenskiy again provided few details while urging troops to keep fighting.
"Thank you to all those who holds their positions and those who advance," he said, citing the eastern and southern fronts, where fighting is heaviest.
Ukraine's general staff said its forces had repelled enemy attacks around Bakhmut and the long besieged town of Maryinka. Russian forces, it said, "continue to suffer heavy losses which they are trying to conceal".
General Oleksander Syrskyi, commander of ground forces who is in operational control of the counteroffensive, posted a picture on social media of an explosion that he said was a group of Russian soldiers being destroyed near Bakhmut.
Ukrainian military spokesman Serhiy Cherevatyi reported new gains near Bakhmut.
"We're trying ... to conduct strikes on the enemy, we are counter-attacking. We've managed to advance up to 1400 metres on various sections of the front," Cherevatyi said.
Britain's Ministry of Defence said Ukraine had conducted "significant" operations in several eastern and southern parts in the last 48 hours, with Russian defences breached in places.
"In some areas, Ukrainian forces have likely made good progress and penetrated the first line of Russian defences. In others, Ukrainian progress has been slower," it said, also characterising the Russian military's performance as mixed.
"Some (Russian) units are likely conducting credible manoeuvre defence operations while others have pulled back in some disorder, amid increased reports of Russian casualties as they withdraw through their own minefields."
