Russia is accusing Washington of preparing a "provocation" in Syria, which would then be blamed on President Bashar Assad's government as alleged use of chemical weapons.
Russian Foreign Ministry spokeswoman Maria Zakharova said on Thursday that Moscow has received information that Syrian rebels have already fabricated video material to accuse Damascus of a chemical attack.
She did not elaborate.
The White House has said Assad is preparing for another chemical attack and warmed that the Syrian ruler will "pay a heavy price" if he unleashes it.
The U.S. in April struck a Syrian air base, which it said had been used to stage a deadly chemical attack. Russia argued that the victims had died of exposure to toxic agents released when Syrian warplanes hit a rebels' chemical weapons depot.