US Defence Department spokesman John Kirby accused Russian President Vladimir Putin of having "utter disregard" for the lives of Ukrainian civilians.
Russia's war in Ukraine is of the "coldest and most depraved sort," Kirby told reporters at his daily briefing on Friday.
"I don't think we fully appreciated the degree to which he would visit that kind of violence and cruelty."
Kirby was responding to a reporter's question about whether he thought Putin was a rational actor.
The Pentagon spokesman said he was not a psychologist and could not assess what was going on in the Russian president's mind, but that "depravity" had been shown toward civilians.
"It's hard to look at what he's doing in Ukraine, what his forces are doing in Ukraine, and think that any ethical moral individual could justify that."
