Russia signed a contract reportedly worth at least $300 million (222 million euros) in 2007 to supply its traditional Arab world ally with a large shipment of the cruise missiles.
Reports said Russia intended to deliver 72 of the missiles to Syria in all.
The deal immediately angered Israel, which fears the weapons may fall into the hands of Hezbollah terrorists
in neighboring Lebanon.
Russia has since also come under growing pressure from Washington, which wants all military sales to President Bashar al-Assad's regime halted because of his deadly crackdown on Syrian street protests.
But Moscow has defended Assad against global pressure and this week argued that its arms sales were permitted under international law and would continue.
Another Russian official told Interfax that the missiles, which operate as part of the Bastion mobile coastal defense system, "will be able to protect Syria's entire coast against a possible attack from the sea."
Each Bastion system is equipped with 36 cruise missiles as well as truck-mounted radar and other equipment.
It was not immediately clear how many of the missiles Russia has delivered to Syria so far.