Story highlights 'I think that they very much feel as if they've been weakened by Assad's actions and their cover up,' Haley said

Haley and the White House now argue that Assad must step down in order to create a stable Syria

Washington (CNN) Nikki Haley, the US envoy to the United Nations, is characterizing Russia as skittish and isolated in the wake of Syrian leader Bashar al-Assad's deadly chemical weapons attack last week that killed scores of civilians, including children.

On Tuesday, US officials charged that Russia was trying to cover up the attack, and Haley said in an interview with CNN's Jamie Gangel 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 realize that ..."

"They knew what was going on?" Gangel asked.

"I think that they knew, yes," Haley said.

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