President Donald Trump's administration accused Russia on Tuesday of trying to shield Syria's government from blame for a deadly gas attack, as Secretary of State Rex Tillerson brought a Western message to Moscow condemning its support for President Bashar al-Assad.
Trump, who has faced criticism for lacking a broader strategy to deal with the Syria crisis, insisted he has no plans to "go into" the war-torn country.
Senior White House officials, briefing reporters on condition of anonymity, said Assad's government carried out the April 4 sarin nerve gas attack on civilians in Syria's Idlib province, killing 87 people including many children, to put pressure on rebels making advances in the area.
Russia has defended the Syrian leader against US allegations that his forces carried out the attack, saying there is no evidence. Russia has blamed Syrian rebels.
"It's clear that the Russians are trying to cover up what happened there," one White House official said.
White House spokesman Sean Spicer later told reporters that the facts backed up the US version of events. "Russia is on an island when it comes to its support of Syria or its lack of, frankly, acknowledgment of what happened," he told reporters.
But at the same briefing Spicer drew criticism after he sought to underscore the ghastliness of the gas attack by saying, "You had someone as despicable as Hitler who didn't even sink to using chemical weapons." Nazi Germany used gas chambers to kill millions of Jews during the Holocaust.
Spicer later apologized and said he should not have made the comparison. "It was a mistake. I shouldn't have done it and I won't do it again," Spicer told CNN in an interview. "It was inappropriate and insensitive."
The White House officials said Russia has frequently offered multiple, conflicting accounts of Syrian government aggression including the incident in the village of Khan Sheikhoun to sow doubt within the international community.