Nikki Haley, US envoy to the United Nations, has characterised Russia as "skittish" and "isolated" in the wake of Syria's deadly chemical weapons attack last week that killed scores of civilians.
On Tuesday, US officials charged Russia with trying to cover up the attack, and Haley said in an interview with CNN that she thinks that Moscow "knew" about it beforehand.
"I think that if you look at the fact that when this information came out, they were so quick to defend," Haley said.
"They didn't look shocked, they didn't look surprised. They were so quick to defend. And then the evidence comes out and we see exactly what it is. And we know exactly what the environment was. Then you realise that …"
"I think that they knew (what was going on), yes," Haley told CNN.
"I think they're nervous… They very much feel as if they've been weakened by Assad's actions and their cover up. They realise the international community didn't buy it and is not buying it," Haley added.
"And they now have to figure out how to save face. We're giving them all the options to save face."
Haley's comments come before critical meetings between Secretary of State Rex Tillerson and Russian Foreign Minister Sergey Lavrov, which were expected to focus on Assad's use of chemical weapons on his own people, said the report.
The former South Carolina Governor also weighed in on comments by White House Press Secretary Sean Spicer, who used Adolf HItler in a criticised analogy to describe the heinousness of Assad's actions.
"It's unfortunate," she said. "We should never have comparisons with Hitler, ever. What I hope Sean was trying to say is just how awful Assad is."
Spicer had said "that even Adolf Hitler had not used the kind of chemical weapons that Syrian President Bashar al-Assad had".
He made the comparison as he tried to condemn Russia's alliance with Assad in the wake of the chemical attack in Syria last week.
"We didn't even use chemical weapons in World War II," Spicer said during a press briefing.