Syria counts Russia as its top legitimate supplier of military equipment. Russia's arms relationship with Syria has been a source of contention among Western allies, though the Russian government said it is committed to its obligations under existing contracts.
Russian presidential aide Yuri Ushakov said Friday there were no plans to deliver missile defense systems to Syria as the conflict escalates.
"The issue has not been raised yet," he was quoted by state news agency RIA Novosti as saying.
Sen. Bob Corker, R-Tenn., ranking member of the Senate Foreign Relations Committee, called Monday on President Obama to provide military assistance to "appropriately vetted" members of the Syrian opposition.
"Official confirmation of [Syrian President Bashar] Assad's use of chemical weapons heightens the urgency for the U.S. to provide the kind of decisive support, including arms and training, to vetted Syrian opposition groups as soon as possible," he said in a Thursday statement.
The White House said Thursday it believes more than 100 people in Syria were killed by chemical weapons, including the nerve agent sarin, launched by pro-government forces.
President Obama has said the use of chemical weapons by Syrian government forces was a "red line" that would trigger U.S. reaction.