Municipal officials in the besieged Ukrainian city of Mariupol have accused Russia of operating mobile crematoria to cover up evidence of war crimes.

“Murderers covering their tracks. Russian mobile crematoriums have started working in Mariupol,” the city council posted on Telegram on Wednesday.

A number of media reports have spoken of Russian mobile crematoria units — incinerators mounted on vehicles — but none have been independently verified so far. Those reports speculated that they were deployed to cover up the deaths of Russian soldiers.

“After the wide international coverage of the genocide in Bucha, the top leadership of the Russian Federation ordered to eliminate any evidence of crimes of its army in Mariupol,” the council added.

“Taking into account the size of the city, the catastrophic destruction, the fierce resistance, tens of thousands civilians could [actually] have been killed by the occupants.”

In a separate statement, Mariupol Mayor Vadym Boychenko said, “The world has not seen the scale of the tragedy in Mariupol since the existence of the Nazi concentration camps. Russia-occupation forces turned our entire city into a death camp.”

Before the Russian invasion, Mariupol had a population of nearly 500,000.

British defense officials said 160,000 people remain trapped in the city by Russian airstrikes and heavy fighting.

A humanitarian-relief convoy accompanied by the Red Cross has been trying without success to get into the city since Friday.