Russia's state-owned RIA Novosti news agency says that the advanced S-400 antiaircraft system has been deployed at a Russian military base in Syria.
Russia announced it would deploy the advanced surface-to-air missile system after Turkey shot down a Russian warplane along the Turkey-Syria border on November 24.
The system has reportedly been deployed in Syria's Lakatia Province, some 50 kilometers from the border with Turkey. It is capable of accurately hitting targets up to 400 kilometers away.
Earlier on November 26, a spokesman for the U.S. Embassy in Moscow said the S-400 deployment "will further complicate an already difficult situation in the skies over Syria."
Spokesman William Stevens told Interfax the S-400s "do nothing to further the fight against ISIL, as they have no air force," using an alternative acronym for the Islamic State (IS) terrorist group.
S-400 AA missile system has been put on air defence combat duty at the Hmeymim airbase. (Russian MoD video)
Stevens added that Washington expected Russia to abide by a bilateral memorandum of understanding on flight safety in the zone of military operations.