The bodies of 44 civilians were found in the rubble of a five-story building in the town of Izium, which is currently controlled by Russian troops, according to the head of the Kharkiv regional military administration.
Oleh Syniehubov said the building had been "completely destroyed by the occupiers" but it's not yet clear when it happened.
Russian forces have been in control of Izium for nearly two months. Before that, the town was heavily contested and intensively shelled.
Syniehubov said that locals who had stayed behind in Izium had excavated the site.
He said there was "no special equipment for dismantling debris, everything is done by hand."
"And of course it does not happen around the clock. When there is no shelling, people come out and try to dismantle those blockages," he added.
What's unclear is whether Russian forces in the area were aware of the operation and permitted the retrieval of the bodies.
Syniebuhov said that, since Izium was occupied, about 1,700 people had been evacuated while what he called a "green corridor" was in existence.
"After that, the occupiers did not allow people to be taken out or humanitarian aid brought there," he added.
He also said that Tsirkuny, a town near Kharkiv, had been liberated and described the scene there as a "total war crime."
"There are a lot of destroyed houses, a lot of office buildings, schools. There are bodies, bodies of civilians," he said.
"The occupiers did not even take their own soldiers, they are on the streets, in private homes and so on. We still have a lot of work to do to clean everything up."
What we know: The Kharkiv Regional Prosecutor's Office said a criminal case "for violating the laws and customs of war, combined with premeditated murder" has been opened.
Between March 7 and 10, the Russian military "systematically shelled the city of Izium. As a result of the shelling, public infrastructure and residential buildings were destroyed," the prosecutor's office said. "So far, the bodies of the victims have been removed from the rubble, and 14 people have been identified."