In October Russia's Foreign Ministry denied media speculation that Moscow would sell the S-300 system, which could help the Islamic republic fend off air strikes by arch foes Israel and the United States on its nuclear sites.
A Foreign Ministry spokesman at the time said that Moscow had no intention of selling weapons to "troubled regions".
But quoting unnamed sources, RIA said on Wednesday that Russia and Iran were holding talks on sales of medium-range air defence systems.
"Moscow has earlier met its obligations on supplying Tor-M1 systems to Iran and is currently implementing a contract to deliver S-300 systems," RIA reported.
The Tor-M1 is a short-range surface-to-air missile system.
RIA did not elaborate on what it meant by fulfilling the contract and the Kremlin had no immediate comment on the report.
The most advanced version of the S-300 system can track targets and fire at aircraft 120 km (75 miles) away. It is known in the West as the SA-20.
Israel, the U.S. and other states suspect Iran is trying to develop a nuclear weapon, using its civilian nuclear programme as a cover. Iran has denied any such intention.
"Russia's military and technical cooperation with Iran has a positive impact on stability in this region," RIA quoted Alexander Fomin, deputy head of Russia's Federal Military Technical Cooperation Service, as saying on Wednesday.
"We have developed, are developing and will continue to develop this cooperation further. The region's security to a large extent depends on this," he added.
"Military and technical cooperation" is an official set phrase used in Russia to denote arms sales.
