Ukraine's President Volodymyr Zelensky has accused Russia of preparing to blow up a dam at a hydroelectric plant in southern Ukraine, which would lead to a "large-scale disaster".

In his overnight address he said the Kakhovka dam on the Dnieper river had been mined by Russian forces, according to Ukrainian information.

The dam is under Russian occupation, but Ukrainian forces are closing in.

Russia has already accused Ukraine of firing missiles at the Kakhovka dam.

The dam also provides Russia with one of the few remaining routes across the Dnieper river in the partially occupied Kherson region.

Russian-installed authorities in Kherson have rejected Ukraine's allegations of a plot to destroy the structure. They blamed Ukrainian forces for an attack on another key crossing, the Antonivskiy Bridge. Four people were killed, including the head of a TV channel, officials said.

Russia began evacuating its proxy authorities in Kherson this week but also said 50-60,000 civilians would leave too, a measure condemned as forced deportations by Kyiv authorities.

Russia's new military commander in Ukraine, Gen Sergei Surovikin, alleged that Ukrainian forces could be planning "banned methods of warfare" in Kherson city and the hydroelectric dam and argued that justified the "evacuation" of the civilian population.

The Institute for the Study of War, an independent US-based think tank, has suggested Russia is "likely continuing to prepare for a false flag attack" on the Kakhovka hydroelectric plant, by creating "information conditions" for Russian forces to blow up the dam after they pull out of western Kherson and then accuse Ukraine of flooding the river and surrounding settlements.

President Zelensky told EU leaders by video on Thursday that Russia had already destroyed more than a third of Ukraine's energy infrastructure, with the aim of creating as many problems with electricity and heating as possible over the winter months. For the first time since the start of the Russian invasion, Ukrainians have been asked to use less electricity, with nationwide limits on usage between 07:00 and 23:00.

If the Kakhovka dam were destroyed, Mr Zelensky warned it could devastate the water supply to much of the south and leave Europe's biggest nuclear plant at Zaporizhzhia without cooling water.

"The dam of this hydroelectric power plant holds a volume of about 18m cubic meters of water," he said. "If Russian terrorists blow up this dam, more than 80 settlements, including Kherson, will be in the zone of rapid flooding. Hundreds of thousands of people could be affected."

The Ukrainian leader also said if the dam were destroyed then the North Crimean Canal would "simply disappear".

The canal, built in 1975, provides Russian-annexed Crimea with a reported 85% of its water supply. An early act in Russia's invasion of Ukraine in February was blowing up a dam that Ukraine had built in the canal after the peninsula was seized in 2014, accusing Russia of not paying for the water.

Several Russian commentators have pointed out that areas under occupation would be worst hit if the Kakhovka dam were destroyed, although dozens of communities under Ukrainian control would be badly affected too.

Pro-Kremlin newspaper Komsomolskaya Pravda said a dam explosion would prompt a 5m-high wave that would wash away all villages beside the Dnieper river at a rate of 25km/h. Within two hours it said the water would hit Kherson city and flood vast areas over three days.

However, presidential office adviser Mykhaylo Podolyak said that mining the dam was all part of a "Surovikin plan" that involved flooding territory to stop Ukraine's counter-offensive.

President Zelensky said that if the Russians were seriously considering blowing up the Kakhovka dam, it meant they realised they would not merely lose control of Kherson but the entire south including Crimea.