Syrian forces are said to control a stockpile of chemical weapons including Sarin nerve agent and mustard gas, among others.
U.S. President Barack Obama warned Monday that U.S. strategic calculus regarding Syria would change if the regime in Damascus deployed chemical weapons.
"It concerns us," he said. "We cannot have a situation where chemical or biological weapons are falling into the hands of the wrong people."
The United Nations has been unable to overcome Russian and Chinese objections to a resolution censuring Syria for the bloodshed. The U.N. Security Council last week voted against extending a mandate for the observer mission to Syria.
Russian counts Syria as one of its top military customers. Russian Col. Vladimir Mandych, deputy director of a Russian agency in charge of chemical weapons, said the Kremlin had no role in that aspect of Syrian defense.
"As far as I know, no Russian-made chemical weapons have ever been supplied to Syria," he was quoted by Russia's state-run news agency RIA Novosti as saying.
Damascus last month threatened to use chemical weapons should foreign forces intervene in the country's civil war.