Harrowing footage has shown Ukrainians being buried in mass graves after 53 people were massacred from one town in a single day.
It comes as Russian forces continue their relentless attacks on civilians across a number of cities.
In the town of Bucha, 53 people were killed in one day - thought to be one of the bloodiest days since war broke out almost four weeks ago.
Emergency services found the bodies of five victims, including three children, buried under rubble during a search of an obliterated residential building.
It comes after 13 people were slaughtered by Russian forces in the city of Chernihiv earlier this week while queuing to buy bread.
It was originally reported that 10 people had died but the death toll has since risen.
There are growing fears the faltering Russian advance, beset by shocking troop and equipment losses, has led to soldiers picking out innocent civilians.
Even before midday yesterday (Weds) three bombers were shot down as it emerged 13,800 Russian troops had died in just 21 days of fighting. Within hours a Russian helicopter was blown out of the sky.
US embassy officials tweeted: “Today, Russian forces shot dead and killed 10 people standing in line for bread in Chernihiv.
“Such horrific attacks must stop. We are considering all available options to ensure accountability for any atrocity crimes in Ukraine.”
Since the attack on civilians queuing for food, Russian forces have also launched an attack on a theatre in the southern city of Mariupol.
Authorities in besieged Mariupol announced that a theatre in the "heart" of the city, which had become a sanctuary for hundreds of civilians, was hit by Russian bombs this afternoon.
The city council said it's "impossible to estimate the scale of this horrific and inhumane act" and that efforts were underway to find the identities of the victims - and just how many innocent Ukrainians were slaughtered.
They confirmed the central part of the venue was completely destroyed, as was the entrance to an area being used as a bomb shelter.
The statement went on: "It is impossible to find words that could describe the level of cruelty and cynicism with which the Russian occupiers are destroying the civilian population of the Ukrainian city by the sea.
"Women, children, and the elderly remain in the enemy's sights.
"These are completely unarmed peaceful people.
"It is obvious that the only goal of the Russian army is the genocide of the Ukrainian people."
They added that Ukrainians will "never forgive" Moscow for "this crazy war".
