It's the latest accusation of war crimes laid at Russia's feet.
On Sunday, Ukrainian officials announced they were investigating allegations that Russian forces had shot and killed unarmed and surrendering Ukrainian soldiers. If confirmed, this would be considered a serious international war crime under the Geneva Convention.
A potential war crime
This comes after footage on social media appeared to show two uniformed men being shot at close range after emerging from a dugout.
The video shows the servicemen, one of them with his hands up, walking out at gunpoint and lying down on the ground before a group of Russian troops appears to open fire. It was not immediately possible to verify the video’s authenticity or the circumstances in which it was filmed, and it was unclear when the incident took place.
Just hours after the Ukraine military press office published an online statement saying the footage was genuine, the case was opened by the country's General Prosecutor's office.
“The video shows a group in Russian uniforms shooting, at point-blank range, two unarmed servicemen in the uniform of the Armed Forces of Ukraine who were surrendering,” the office said in a Telegram update later the same day.
As of Sunday evening, there were no public statements from the Russian government or military on the video.
Kyiv, its Western allies and international human rights organizations have repeatedly accused Moscow of breaching international humanitarian law since it launched its full-scale invasion of Ukraine in February 2022. The Kremlin denies these allegations.
Families rally for Ukrainian soldiers in Kyiv
As the country's defensive war against Russia enters its second winter, families of Ukrainian soldiers rallied in Kyiv to call for relief.
Some called for the return of captive troops, while others questioned how much longer the exhausted soldiers could endure the daily battle.
Many of the relatives are calling for fixed terms at the front and abolishing open-ended military service.
The demonstration was organised by the Azovstal Families organisation which continues to call for the prisoner's release.
"We're fighting for our prisoners of war, our Azovstal defenders and others," Katerina Prokopenko, the founder of the Azovstal Families Association, said as she attended the gathering.
Ukrainian President Volodymyr Zelenskyy said prisoner exchanges with Russia have slowed in the past few months.
Since the start of the war "several thousand" people had returned home, he told the Associated Press, "but more, another several thousand are still in captivity”.
Russia took control of Mariupol in May last year after a nearly three-month siege that reduced much of the strategic port city to a smoking ruin.
Ukrainian fighters held out in the Azovstal steel plant for weeks before their government ordered them to abandon the plant’s defence and save themselves.
As they surrendered, troops were taken prisoner by Russia.
Kherson region hit by a wave of Russian shelling
At least two people died and seven more were wounded after Russian forces on Sunday shelled a high-rise apartment block and other civilian buildings in the Kherson region.
Also on Sunday, Ukraine’s energy ministry reported that close to 1,000 towns and villages suffered power outages that day, with hundreds of settlements in the west battered by wintry weather and others affected by ongoing fighting.
The Institute for the Study of War, a Washington-based think tank, late on Saturday assessed that military operations have slowed down all along the frontline in Ukraine due to poor weather, with mud bogging down tracked vehicles and making it hard for lighter equipment and infantry to advance.