The remains of two children are among 146 bodies exhumed at a mass burial site close to the city of Izyum in eastern Ukraine, according to an official.
Many of the victims are civilians, with some feared to have been tortured while enduring a violent death, authorities said on Monday.
The mass burial site containing 440 graves was found after the city was liberated from Russian control by Ukrainian forces.
Ukraine latest: Zelenskyy declares there will be “no lull” in resistance after rapid gains in Kharkiv
The city was reclaimed following a counter-offensive in the Kharkiv region.
The Kharkiv governor, Oleh Synehubov, said two children were among the bodies in Izyum.
“Some of the dead have signs of a violent death,” he said.
“There are bodies with tied hands and traces of torture.”
“The deceased were also found to have explosive, shrapnel and stab wounds,” he added.
Forensic experts wearing white protective suits and rubber gloves have spent days painstakingly exhuming and identifying the bodies buried in makeshift graves marked with flimsy wooden crosses.
President Volodymyr Zelenskyy was pictured in the newly-recaptured city raising his country’s blue and yellow flag in a show of triumph last Wednesday.
Following the discovery of the burial site, Mr Zelenskyy’s chief of staff, Andriy Yermak, branded Russia a “murderer country” and a “state sponsor of terrorism”.
Kremlin spokesman, Dmitry Peskov, rejected Ukraine’s allegations as a “lie”.
In his nightly address to the nation last Thursday, Mr Zelenskyy said: “We want the world to know what is really happening and what the Russian occupation has led to.
“Bucha, Mariupol and now, unfortunately, Izyum.
“Russia leaves death everywhere. And it must be held accountable for that. The world must hold Russia to real account for this war.”
US President Joe Biden previously branded Russian leader Vladimir Putin a “war criminal” over civilian killings in Bucha, outside the capital Kyiv.
Some were shot in the head with their hands tied behind their back, according to Ukrainian officials.
But Moscow has categorically denied being responsible for the massacre.
Meanwhile, photos from Mariupol revealed how the besieged city was left “completely devastated” after weeks of relentless bombardment at the hands of Kremlin troops.
Dozens of people sheltering in a theatre died in the wake of a reported Russian airstrike – despite the building being marked with the word ‘children’ in an attempt to deter an aerial attack.