The US says Russia is ignoring "the facts" in Syria when it doubts that the government, rather than rebels, was behind a chemical weapons attack.
Russian Foreign Minister Sergei Lavrov said Tuesday that Moscow believes the August 21 gassing was a "provocation".
The sparring comes even after the US and Russia reached a sweeping weekend agreement designed to rid Syria of chemical weapons by mid 2014. That surprise deal headed off US military strikes that had seemed imminent just two weeks ago as a way to punish Damascus for the chemical attack and prevent another.
A UN report released Monday says chemical weapons were used in Syria, but it avoided saying by whom.
But the US and its allies are fervent in their belief that the forces of President Bashar al-Assad used the banned chemical weapons against its own civilians.
"He's swimming against the tide of international public opinion, but more importantly, the facts," State Department spokeswoman Jennifer Psaki said, referring to Lavrov.
The UN report, "confirms unequivocally that chemical weapons, including the nerve agent sarin, were used in Syria. We all know that. But based on our preliminary view of information contained in the report, several crucial details confirmed the Assad regime's guilt in carrying out this attack," Psaki said.
