President Vladimir Putin says Russia has not yet sent S-300 antiaircraft missile-defense systems to Syria.
Putin was speaking at a joint press conference with EU leaders after a summit in the Urals city of Yekaterinburg.
"The S-300 is, indeed, one of the best antiaircraft missile systems in the world -- probably the best one. It is, of course, a very serious weapon," Putin said. "We do not want to upset the balance in the region. The contract [with Syria] was signed several years ago. It has not been implemented yet."
Western nations have intensified their criticism of the planned sale of S-300 missiles to Syria since Syrian President Bashar al-Assad appeared to suggest in an interview last week that a first shipment of the antiaircraft defense systems may already have been delivered to his forces.
Putin defended Russia's arms sales to Assad's government, saying they are in line with international law.
He also criticized the EU's decision not to extend its embargo on weapons sales to rebels fighting to topple Assad's regime. He warned against foreign military intervention, saying it will not resolve the more than two-year-old conflict that has claimed more than 80,000 lives.
The Syrian crisis dominated Putin's talks with EU Council President Herman Van Rompuy and European Commission President Jose Manuel Barroso, which also covered bilateral trade issues.
At the June 4 press conference, Putin denied there was discrimination against homosexuals in Russia, but he said he would back a proposed ban on the adoption of Russian children by foreign gay couples.
"As for a law restricting adoptions from Russia by same-sex couples, I haven't seen such a bill yet," he said. "If parliament passes such a bill, I will sign it."
Prior to the summit, the European Commission had said EU leaders would bring up concerns about Russia's human rights record.
With reporting by Reuters and AP