Kremlin officials said Friday they would build up defenses and turn the southern Ukrainian city of Kherson into a “fortress” while Kiev’s troops advance and Russia pulls residents out of the region.

The allegation came as Ukrainian President Volodymyr Zelenskyy said Russian troops were preparing to destroy a hydroelectric power station in the southern Kherson region in what would amount to a “large-scale disaster”.

Ukrainian forces have been advancing along the west bank of the Dnieper River towards the region’s capital, also known as Kherson, in recent weeks, supported by Western weapons.

Kherson was the first major city to fall to Moscow’s troops since the February invasion began, and its recapture would be a crucial prize in the Ukrainian counteroffensive.

Moscow authorities in Kherson said Kiev forces killed four people on Friday when they shelled the Antonivskiy Bridge over the Dnipro River for civilians to cross ahead of an expected Ukrainian attack.

“Four people were killed,” pro-Moscow official Kirill Stremousov said on Telegram. “The city of Kherson, like a fortress, is preparing for its defense.”

A Ukrainian military spokeswoman, Nataliya Gumenyuk, denied that Kiev’s forces were responsible, saying their forces are not targeting the local population.

Russian state media had aired footage in recent days showing civilians carrying bags boarding ferries across the river from Kherson.

Kyiv has branded the organized movement of Kherson residents to Russia and other Moscow-controlled regions as “deportations” of Ukrainian citizens.

Zelenskyy said late Thursday that Russian forces had mined the Kakhovka hydroelectric power station with the intention of blowing it up.

Hundreds of thousands of people around the lower Dnipro River would be threatened by flash floods if the dam were to be destroyed, Zelenskyy warned in a speech to European leaders on Thursday.

He said the disruption to water supplies in the south could also affect the cooling systems at the Zaporizhia nuclear power plant, Europe’s largest.

The nuclear facility is a major concern of the eight-month Russian invasion, during which both sides regularly accuse the other of shelling nearby and endangering operations.

Ukraine’s push south comes after a full-scale counteroffensive in the northeastern region of Kharkiv that severely disrupted Russia’s supply routes and logistics corridors in the eastern Donbass region.

But Russian forces continued to shell the region’s largest city, Kharkiv, and the presidency said on Friday that “industrial infrastructure” in the city was hit, wounding six.

The attack in the last week-long barrage targeting infrastructure and particularly power plants.

Energy saving measures have been rolled out across the country after Russian missile and drone strikes destroyed more than 30 percent of the country’s power plants in a week, Zelensky said.

A 64-year-old Ukrainian, Vyacheslav, told AFP in Kyiv that the nation will get by despite the restrictions.

“There are books to read. There are battery powered lamps. I think we can last a few hours. There are gas stoves so you can still cook,” he said, but refused to give his last name.

Kyrylo, a 27-year-old shop clerk, said there has been a rush for power banks after Russian attacks on power plants in the capital began.

“We do not sell flashlights, but in terms of power banks, I can say that on the 10th, when the attack on Kyiv began, almost all available power banks were sold, and in general the demand for power banks increased by 70 or 80 percent.

The Ukrainian presidency said on Friday that Russian forces continued shelling sections along the entire Donbass front line in eastern Ukraine and that two people were killed in the Donetsk region.