Russia has been accused of committing war crimes after hundreds of bodies were discovered in Bucha, a town on the outskirts of the Ukrainian capital of Kyiv.
ABC reports the death toll sits at 410, however Ukrainian officials have warned there is a significant number of residents still considered missing, so that number is likely to rise.
Ukrainian officials have finally been able to access the towns of Bucha, Irpin and Hostomel for the first time after Russian forces withdrew from areas around the capital.
Prosecutor General Iryna Venedyktova said more time is needed to work out the extent of the crimes.
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"We need to work with witnesses," Ms Venedyktova said, adding some are so traumatised that they are unable to speak.
Ukraine is now building a case against Russia for war crimes following the massacre, with President Volodymyr Zelenskyy calling the mass slayings as 'genocide'.
"Hundreds of people were killed. Tortured, executed civilians. Corpses on the streets. Mined areas. Even the bodies of the dead were booby-trapped," Zelenskyy said.
Adviser to the Ukrainian President, Oleksiy Arestovych, said the carnage discovered in the towns north-west of Kyiv was like a 'scene from a horror movie'.
Russia has denied all the allegations against them relating to Bucha and even threw an allegation back to Ukraine.
Moscow claims Ukrainian forces in Kyiv staged the horrifying scenes for Western media in the hope it would damage Russia's reputation.
The Kremlin claims no residents in Bucha suffered any violence from their soldiers.
The sheer enormity of the kills have been captured on satellite imagery, with mass graves now seen from the sky above Bucha.
One witness recounted Russian soldiers going from building to building, hunting for civilians huddled in basements and dragging those they found into the streets or shooting them, according to ABC reports.
The European Union and United Kingdom have condemned the reports of the civilian massacre.
“Reports of Russian forces targeting innocent civilians are abhorrent. The UK is working with others to collect evidence and support @IntlCrimCourt war crimes investigation. Those responsible will be held to account,” Britain’s Foreign Secretary Liz Truss said on Twitter.
The EU has vowed to impose further sanctions on Russia following the savage slayings.
"Shocked by haunting images of atrocities committed by Russian army in Kyiv liberated region," president of the EU Council Charles Michel said.
"Further EU sanctions and support are on their way."
Mr Michel said the EU was assisting Ukraine and non-governmental organisations to gather the evidence needed to prosecute Russia for crimes in the international courts.
The grim discovery comes as Russian forces retreat from towns surrounding the capital which has seen heavy fighting since Putin's forces invaded on February 24.
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Rachel Lang