The office of Ukraine’s Prosecutor General says it has opened a criminal investigation after a video emerged earlier this week appearing to show Russian soldiers executing six unarmed Ukrainian prisoners of war.

“According to preliminary data, during an assault on the positions of Ukrainian troops in Donetsk region, the occupiers captured six servicemen of the Ukrainian Defense Forces and subsequently shot them dead,” the Prosecutor General’s office said in a January 23 statement. “The execution of prisoners of war is a serious violation of the Geneva Convention relative to the Treatment of Prisoners of War and is classified as a grave international crime. Investigative actions are currently underway to establish all the circumstances of the crime and the persons involved in its commission.”

The video, which has circulated widely on social media since January 23, shows what appear to be Russian soldiers taking turns shooting six unarmed Ukrainian POWs in their backs.

CBS News has not been able to independently verify the video. The six men seen in the clip haven’t been identified by Ukrainian authorities, but the yellow armbands they appear to have been wearing are consistent with those worn by Ukrainian forces operating in the region. 

The video appears to show the men being shot just outside a dugout, which lends credibility to the prosecutor general’s assertion that they were killed after being captured during an assault.

Before the video stops, one of the Russian soldiers says: “One is mine,” and a seventh soldier is shown on the ground, but his condition is not clear.

The Ukrainian government’s Ombudsman, Dmytro Lubinets, said he had filed a war crimes claim with the United Nations and the International Committee of the Red Cross over the incident shown in the video.

“The Russian army has never been known for its decent treatment of prisoners of war, and once again it demonstrates its helplessness and criminality,” Lubinets said in a statement. “The lack of accountability has turned the crime into a system. We cannot turn a blind eye to this! Ukraine needs justice and accountability for those who commit crimes and do not comply with any norms!”

The allegations against the Russian forces come as President Vladimir Putin’s nearly three-year invasion of Ukraine grinds on, with his troops making small but steady territorial gains across Eastern Ukraine’s Donbas region.

On Tuesday, Russia’s military claimed troops had recaptured the village of Dvorichna, near the northeastern city of Kharkiv. Russian forces first seized the village not long after Putin launched the full-scale invasion in February 2022, but it was retaken by Ukrainian forces months later during a counter-offensive.

The war has shown no signs of easing despite President Trump taking office for a second term in the U.S., after repeatedly claiming he could end the war within days. 

Many Ukrainians, and their backers in Europe, have worried that Mr. Trump could pressure Ukraine, by withholding vital U.S. military aid, into accepting a negotiated truce with Russia that would allow Putin to retain a significant part of the territory his forces have occupied.

As CBS News’ Holly Williams reported Tuesday, a recent poll shows a slim majority of Ukrainians now support a negotiated ceasefire with Russia — a major shift since the early days of the war — but the government and many civilians say any deal must include guarantees for Ukraine’s security, such as European peacekeepers on the ground or NATO membership.