Starving children were forced to survive by eating their pets after Russian troops fled from their village, a Ukrainian official has claimed.
Tymofiy Mylovanov, an advisor to Ukrainian President Volodymyr Zelensky, has shared a litany of horrific war crime allegations which are being investigated.
It comes as pressure mounts to hold Russian leaders responsible for the horrors they unleashed following February's invasion.
At the weekend details emerged of summary execution of civilians, torture and rape as a "weapon of war" by Vladimir Putin's forces.
Mr Mylovanov said that atrocities in Brovary and Chernihiv might be more "heinous" that those in Bucha - where Russian troops have been accused of carrying out "genocide".
In a heartwrenching thread appealing for Ukrainians to share their experiences in order to document the war crimes, he wrote: "(In) Holodomor in a village in Chernihiv region (Russians) took away all food.
"People survived on what they had hidden, pets..."
Mr Mylovanov said that he had been told about a boy being burned alive by killers who poured a Molotov cocktail on him and set him on fire.
The Presidential adviser said he had heard reports of mass rapes followed by summary execution in a village which had been under Russian control.
In another instance he said families had been executed in the fields where they worked, according to eyewitnesses who had seen the bodies.
He urged people who had seen the brutality of Vladimir Putin's troops to report war crimes.
Mr Mylovanov said: "We are collecting phone numbers and contact info of those who are willing to talk, the names of the villages, locations."
Investigations have been launched into allegations of war crimes by Russian forces.
Experts say it is likely that Russians accused of war crimes will be tried in Ukrainian courts, although being hauled in front of an international court is a "possibility".
However Putin is unlikely to face legal consequences for the terror he has unleashed unless he is ousted and his successor opts not to protect him.
A horrifying litany of brutal murders, torture and rape have come to light amid accusations of genocide, with Ukraine's foreign minister branding the invaders "worse than ISIS".
Heartbreaking images from the city of Bucha show bodies lying on the street, with many said to have been shot while their hands were bound.
A report by Human Rights Watch said Russian forces had carried out "unspeakable, deliberate cruelty and violence" directed toward the Ukrainian population.
