Ukraine's government has accused the Russian military of abducting another mayor in an area that it has captured.
Yevhen Matveyev was seized in the southern town of Dniprorudne, Ukrainian Foreign Minister Dmytro Kuleba tweeted, accusing Russia of "terror" tactics.
Earlier, Russia installed a new mayor in Melitopol, after allegedly abducting the city's previous incumbent.
Ukraine's president also accused Russia of trying to create "pseudo-republics" to break his country apart.
In her first public appearance, Melitopol's newly installed mayor Galina Danilchenko urged residents not to take part in "extremist actions" and declared her main task was construction of "basic mechanisms under the new reality".
Hundreds of people took part in a protest outside the city hall on Saturday to demand the release of previous incumbent Ivan Fedorov, who had refused to co-operate with Russian troops since they took the city on the third day of the invasion.
In Melitopol, defiant residents gathered near occupied district administration demanding that Russians release the kidnapped Melitopol mayor Ivan Fedorov - video by Odessa reg governor Maksym Marchenko pic.twitter.com/nCrE6OtQd0— Myroslava Petsa (@myroslavapetsa) March 12, 2022
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Mr Fedorov was last seen on Friday evening being dragged away from the city's crisis centre by several armed men with a bag over his head.
"We are not co-operating with the Russians in any way," Mr Fedorov had told the BBC earlier in the week. "They have not tried to help us, they cannot help us, and we do not want their help."
Russian authorities have not commented on his disappearance, but the prosecutor's office of the Russian-backed breakaway eastern Ukrainian region of Luhansk has reportedly accused him of "terrorist activities".
Ukrainian President Volodymyr Zelensky has demanded Mr Fedorov's immediate release and asked the leaders of Israel, Germany and France to put pressure on Russia to free him.
In his latest video address on Saturday night, Mr Zelensky said Russia was to create "pseudo-republics" in Ukraine.
He praised those refusing to collaborate in the Russian-controlled Kherson region.
The council there had earlier adopted a resolution reaffirming that it "has been, is and will be an inalienable part of the united state of Ukraine" in response to what it said was a Russian plan to stage a referendum on the creation of a "people's republic".
Mr Zelensky also warned "certain figures" of dire personal consequences of any collaboration - an apparent reference to Ms Danilchenko.