Russian troops shot dead the mayor of Motyzhyn, a town 30 miles west of Kyiv, along with her husband and son, according to claims from local residents.
The bodies were reportedly thrown into a pit in a pine forest behind houses where Russian forces had slept, The Associated Press said.
The mayor’s husband had his hands behind his back, with a piece of rope nearby, and a piece of plastic wrapped around his eyes like a blindfold, the news agency reported.
Journalists found four bodies inside the pit, all of whom seemed to have been shot at close range.
Ukraine’s deputy prime minister Iryna Vereshchuk said that the mayor, Olga Sukhenko, had been killed while being held by Russian forces.
She added in a video message posted on her Telegram account that eleven other local community leaders across the country have been kidnapped by the Russian army.
Speaking on Sunday, Ms Vereshchuk said: “Up to today, 11 heads of local communities in the regions of Kyiv, Kherson, Kharkiv, Zaporizhzhia, Mykolaiv and Donetsk are in captivity.
“We are informing the International Committee of the Red Cross, the UN, all possible organisations, just like for the other civilians who have disappeared.”
Polish prime minister Mateusz Morawiecki said on Monday that the discovery of civilians’ bodies in Bucha and Irpin, some with their hands tied behind their backs, should be classified as a genocide.
Mr Morawiecki said Russia’s invasion was “pure evil” and supported the establishment of an international commission to investigate Russian crimes committed in Ukraine.
French president Emmanuel Macron said there were “clear indications of war crimes” in Bucha, and called for further sanctions on Russia.
The Ukrainian government has accused Russia’s armed forces of carrying out a “genocide”.
Ukraine’s foreign minister, Dmytro Kuleba, said: “[The] Bucha massacre was deliberate. We are still gathering and looking for bodies, but the number has already gone into the hundreds.
“Dead bodies lie on the streets. They killed civilians while staying there and when they were leaving these villages and towns.”
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