The bodies of two small children have been recovered from a mass grave outside Kyiv where Ukrainian authorities say at least 55 people were found dead, having been “shot, set on fire, and crushed by tractors.”

The grisly details were shared Wednesday in a video interview with a local police officer taking part in the exhumation of bodies in the suburb of Bucha, where hundreds of civilians were killed during the Russian occupation.

Anton Gerashchenko, an adviser to Ukraine’s interior minister, confirmed the discovery in a statement on Telegram.

“They shot them, set them on fire, and crushed them with tractors. All investigative actions will be recorded on video as evidence of the Russian occupiers’ crimes against humanity,” Gerashchenko wrote.

The victims have not yet been identified, but authorities say a 4-year-old boy and 10-year-old boy were found alongside a woman thought to be their mother. Most of the victims had gunshot wounds to their heads.

More than 400 civilians were found dead after Russian forces retreated from the area last month, according to Ukrainian authorities, who say they are compiling evidence of Russian war crimes. Survivors have given chilling accounts of the troops opening fire on fleeing families and gunning down residents at random.

Oleksandr Chikmarev, a Bucha resident who says he tried to flee the suburb with his family on March 6, spoke from a hospital bed in a video shared by Ukrainian media outlets.

“We were leaving the house and a [Russian military vehicle] stopped right across from us. I stopped the car…. And they immediately opened fire. My kids and wife died right away,” he said, covering his face as he began to break down.

“My eldest was 10, and the younger one was 5.… They killed my family right before my eyes.… Why did they need to shoot? They saw it was a family driving, little kids,” he said.

Despite mounting evidence of the slaughter of civilians in Bucha, Russian authorities have repeatedly claimed the deaths were “staged” by Ukrainian forces and their Western allies. Many fear the scale of alleged war crimes in the town will only be surpassed by what has been happening in other besieged cities, particularly Mariupol, where Ukrainian troops have spent weeks holding back a full-blown Russian takeover.

On Wednesday, after Ukrainian marines there issued a desperate video appeal for help, saying they were out of supplies and “surrounded,” Russia’s Defense Ministry claimed 1,026 Ukrainian troops had “laid down their weapons” and surrendered.

But the Ukrainian presidential administration immediately denied that, saying the 36th Marine Brigade had managed to break free from Russian encirclement and join forces with Azov fighters.

“The defenders of the city, now already jointly, have seriously strengthened their defense of the region,” Oleksiy Arestovych, an aide to the Ukrainian president, said in a statement on Facebook.