Washington's envoy for war crimes, Beth Van Schaack, 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.

"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 in a briefing with reporters, though she also pointed out that the scale of criminality exhibited by Russian forces was "enormous" compared to the allegations against Ukrainian troops.