Vladimir Putin has warned the West against taking one-sided action in Syria but also said Russia "doesn't exclude" supporting a U.N. resolution on punitive military strikes if it is proved that Damascus used poison gas on its own people.
However, the Russian president added any military strikes without UN approval would be "an aggression".
In a sensational interview with The Associated Press and Russia's state Channel 1 television, Putin said Moscow has provided some components of the S-300 air defence missile system to Syria but has frozen further shipments.
He suggested that Russia may sell the potent missile systems elsewhere if Western nations attack Syria without U.N. Security Council backing.
US President Barack Obama has called for punitive action in response to an alleged chemical weapons attack.
Putin said it was "too early" to talk about what Russia would do if America took action without a UN resolution.
He also called allegations that Syrian President Bashar al-Assad attacked rebel forces with chemical weapons "ludicrous"
"From our viewpoint, it seems absolutely absurd that the armed forces, the regular armed forces, which are on the offensive today and in some areas have encircled the so-called rebels and are finishing them off, that in these conditions they would start using forbidden chemical weapons while realising quite well that it could serve as a pretext for applying sanctions against them, including the use of force," Putin said regarding the allegations against Assad – a staunch ally of Russia.
The Obama administration says 1,429 people died in the Aug. 21 attack in a Damascus suburb, while Assad's government blames the episode on rebels trying to overthrow him.