Russia is accused of kidnapping a second mayor in the southern Ukraine.
Yevhen Matveyev was taken in Dniprorudne – a town he represents – in the Zaporizhzhia region, at 8.30am on Sunday, according to the Ukrainian government.
President Volodymyr Zelensky said: “It is a crime against democracy. I assure you that 100 percent of people in all democracies know about it.
“The actions of the Russian invaders will be equated with the actions of the Islamic State terrorists.”
Foreign minister Dmytro Kuleba also accused Vladimir Putin’s regime of resorting to “terror” tactics since invading Ukraine on 24 February.
Earlier, Russian troops were accused of kidnapping Melitopol mayor Ivan Fedorov before installing the Kremlin’s choice Galina Danilchenko.
Hundreds of people protested outside Melitopol city hall this weekend to demand the release of Mr Fedorov, who has refused to co-operate with Russian troops since they seized the city on the third day of the invasion.
Mr Fedorov was last seen on Friday evening with a bag over his head being taken from the city’s crisis centre by armed men.
Ukrainian officials, when sharing CCTV footage of the incident, said the armed men were Russian soldiers.
The breakaway pro-Russia state of Luhansk, in eastern Ukraine, reportedly accused Mr Fedorov of “terrorist activities”.
Before his disappearance, Mr Fedorov has told the BBC: “We are not co-operating with the Russians in any way.
“They have not tried to help us, they cannot help us, and we do not want their help.”
Mr Zelensky has demanded Mr Fedorov’s immediate release and asked the leaders of Israel, Germany and France to urge Russia to free him.
In his video address on Saturday night, the Ukrainian president confirmed that Kyiv suspects Russia plans to create “pseudo-republics” in Ukraine to divide and conquer it.
Mr Zelensky praised those refusing to collaborate in the Russian-controlled Kherson region.
Russia has not commented on Mr Fedorov’s disappearance, that comes after the Melitopol council had adopted a resolution stating it “has been, is and will be an inalienable part of the united state of Ukraine”.
The statement was in response to, what it said was, Putin’s plan to stage a referendum on the creation of a “people’s republic” in Melitopol.
Also in Melitopol, local activist Olha Haisumova was abducted during the city hall rally, according to Ukrainian news outlet Ukrinform. Local resident Serhiy Kirichuk was also kidnapped, the report adds.