Mr Kuleba told Times Radio: “We understand they were killing civilians while leaving, while withdrawing, while staying there in this town of Bucha and also in other towns and villages in key regions, but also while withdrawing from them out of anger and just because they wanted to kill.

“There was no good reason for them. These were not guerrillas, they were not people opposing them. It remains to be seen based on the evidence collected whether these crimes will qualify for the crimes of genocide.”

Oleksiy Arestovych, an adviser to Mr Zelensky, said liberated cities had revealed a “post-apocalyptic picture” of life under Russian occupation.

He said: “Victims of war crimes have already been found, including raped women who they tried to burn, local government officials killed, children killed, elderly people killed, men killed, many of them with tied hands, traces of torture and shot in the back of the head. Robberies, attempts to take gold, valuables, carpets, washing machines.”

Ukrainian officials also said Russian troops are holding 11 of the country’s mayors and had killed one in detention.

In a message posted on social media, Iryna Vereshchuk, the deputy prime minister, said local leaders from the Kyiv, Kherson, Mykolaiv and the Donetsk regions “are in Russian captivity”.

On Saturday, Mr Zelenksy warned that retreating Russian troops were creating a “catastrophic” situation by leaving mines around the bodies of those killed, as well as abandoned equipment and homes.