Russia has been accused of committing war crimes in the town of Bucha, just north of Kyiv, which was recently liberated by Ukrainian forces.
Facebook owner Meta Platforms Inc briefly restricted hashtags related to civilian deaths in northern Ukraine, where bodies of people allegedly shot at close range were found in a town evacuated by Russian forces, a company spokesman confirmed on Monday.
The killings in Bucha, outside Kyiv, have drawn pledges of further sanctions against Moscow from the West.
Among the wrecks of burned-out armoured vehicles, images of dead bodies lining the streets of the town were evidence of a deliberate "massace of civilians," Ukraine said on Sunday in what is being described as war crimes committed by the Russian army.
Meta spokesman Andy Stone said automated systems that scan for violent imagery on Facebook and Instagram, which the company also owns, were responsible for blocking hashtags including #bucha and #buchamassacre.
"This happened automatically because of the graphic content people posted using these hashtags. When we were made aware of the issue yesterday, we acted quickly to unblock the hashtags," he wrote on Twitter.
Facebook content deleted if explicit
Facebook and Instagram permit the posting of graphic and violent content when it is shared to raise awareness of possible human rights abuses, but delete the content if it is extremely explicit or celebrates suffering.
The social media company also adds warning labels to some graphic posts that users must click through before they can see the images.
Human rights groups have critised Meta's approach to removing violent content during conflicts, saying its practice of purging the data from its servers after 90 days results in the deletion of critical evidence of war crimes.
Stone said Meta was "exploring ways to preserve this type and other types of content when we remove it," specifically in relation to the war in Ukraine.
Russia has denied any accusations related to the murder of civilians.