Washington's envoy for war crimes said on Monday the United States was monitoring allegations of Ukrainian forces summarily executing Russian troops, and said all parties should face consequences if they commit abuses in the conflict.
Russia's defense ministry on Friday cited videos circulating on social media that allegedly showed Ukrainian soldiers executing Russian prisoners of war.
"We are obviously tracking that quite closely," Beth Van Schaack, the US ambassador-at-large for global criminal justice, told reporters during a telephone briefing.
"It's really important to emphasize that the laws of war apply to all parties equally: both the aggressor state and the defender state and this is in equal measure," she said, adding that "all parties to the conflict must abide by international law or face the consequences."
The videos show what appear to be Russian soldiers lying on the ground after apparently surrendering. Then automatic gunfire rings out and the video shows around 12 bodies.
Ukraine's deputy prime minister has reportedly said Ukraine will investigate the incident. The country's commissioner for human rights, Dmytro Lubinets, said the videos appeared to show "a staged capture" where Russian forces were not truly surrendering.
Russia has been accused of numerous war crimes since its full-scale invasion of Ukraine in February, including by operating a system of so-called filtration camps to move Ukrainians in occupied areas into Russia. Russia has denied the allegations and accused Ukraine and its backers in the West of fabricating the claims.
Van Schaack said the scale of criminality exhibited by Russian forces was "enormous" compared to the allegations against Ukrainian troops, and noted that the two sides responded differently when allegations of atrocities surface.
"Russia inevitably responds with propaganda, denial, mis- and dis-information, whereas Ukrainian authorities have generally acknowledged abuses and have denounced them and have pledged to investigate them."