Russia has begun delivering S-300 air defense missile systems to Iran.
The announcement was made on December 3 by the arms trade adviser to President Vladimir Putin.
However, Vladimir Kozhin did not disclose any details in comments quoted by Russia's TASS news agency.
Russia in 2010 froze a deal to supply advanced long-range S-300 missile systems to Iran, linking the decision to UN sanctions.
Putin lifted the suspension earlier this year following Iran's deal with six world powers to curb its nuclear program in exchange for relief from international sanctions.
Last month, officials said that Russia and Iran finalized the contract for their delivery.
The S-300 deal has long worried Israel and other countries in the region, as well as the United States, which see it as destabilizing.