Ukraine launched an investigation on Wednesday into a gruesome video circulating on social media that purportedly shows the beheading of a Ukrainian soldier.

The video spread quickly online and sparked outrage from Ukrainian officials. The Kremlin called the footage “horrible” but said it needed to be verified.

The Associated Press was not able to verify the authenticity of the video or the circumstances of where and when it was shot.

Meanwhile, a Russian defence official claimed that fighters from Russia’s paramilitary Wagner group have seized three districts of Bakhmut, the embattled city that for months has been the focus of Moscow’s grinding campaign in the east.

The video circulating online appears to show a man in green fatigues wearing a yellow armband, typically donned by Ukrainian fighters. He is heard screaming before another man in camouflage uses a knife to decapitate him.

A third man holds up a flak jacket apparently belonging to the man being beheaded. All three men speak Russian.

Since Russia’s forces invaded Ukraine more than a year ago, they have committed widespread abuses and alleged war crimes, according to the UN, rights groups and reporting by The Associated Press.

Ukraine has accused Russia of targeting apartment buildings in its strikes, and images of hundreds of civilians lying dead in the streets and in mass graves in Bucha, after Russian forces withdrew, have horrified the world.

The International Criminal Court has issued an arrest warrant for Russian President Vladimir Putin for war crimes.

The Kremlin denies it has committed war crimes or that it has targeted civilians.

Ukrainian troops have also been accused of abuses, and last year Kyiv said it would investigate video footage circulated online that Moscow alleged showed Ukrainian forces killing Russian troops who may have been trying to surrender. Ukrainian President Volodymyr Zelenksy said the violence in the latest video would not be forgotten.