The Moscow-appointed government in the occupied Ukrainian region of Kherson has suspended plans for a referendum on joining Russia as Ukraine continues its counter-offensive to retake the territory.
Kirill Stremousov, deputy head of the Kherson administration, said the plans were put on hold because the security situation, Tass news agency reported.
He said a road bridge over the Dnipro river had become impassable after weeks of Ukrainian shelling.
Russian officials wanted to hold referendums in several occupied regions, including the self-proclaimed Donetsk and Luhansk People's Republics, alongside elections in Russia.
Ukraine and its allies have denounced the referendum plans.
Ukraine said its forces have seized control of Vysokopillya, a town about 150 kilometres north-east of Kherson City, which was captured by Russia in the early days of the war.
Kyrylo Tymoshenko, deputy head of President Volodymyr Zelenskyy's office, posted an image on Facebook that showed soldiers raising the Ukrainian flag in Vysokopillya.
His caption read: "Vysokopillya, Kherson region. Ukraine. Today."
On Monday, Ukraine told people in the Crimean Peninsula, which Russia annexed in 2014, to prepare bomb shelters and stock up on supplies as it continued its push in the east.
"We ask residents of occupied territories, including the Crimean Peninsula, to follow [Ukrainian] officials' recommendations during de-occupation measures," said presidential adviser Mykhailo Podolyak.
"In particular, to prepare a bomb shelter, stock up with sufficient amounts of water and charge powerbanks. Everything will be Ukraine."
The announcement came as the sole remaining reactor at the Zaporizhzhia nuclear power station was knocked offline again on Monday as nearby shelling disrupted power lines.
Referring to information supplied by Ukraine, the International Atomic Energy Agency said the plant's backup power line was cut to extinguish a fire.
The line was not damaged and would be reconnected, it said.
The UN nuclear watchdog said the plant had enough electricity to operate safely and would be reconnected to the grid once backup power was restored.
Mr Zelenskyy blamed the incident on Russian shelling and said it put the site "a step away" from a nuclear disaster.
"Again — already for the second time — because of Russian provocation, the Zaporizhzhia station was placed one step away from a radiation catastrophe," he said.
Ukrainian Energy Minister German Galushchenko said "the world is once again on the brink of a nuclear disaster".
"The de-occupation of the ZNPP and the creation of a demilitarised zone around it is the only way to ensure nuclear safety," he said.
Six inspectors from the UN agency arrived at Zaporizhzhia last week to assess safety at the plant.
Two members remain at the site to monitor operations.
The watchdog's chief Rafael Grossi will issue a report on Ukraine, including the plant, on Tuesday and brief the UN Security Council, the agency said.