Western officials and a Russian source said a Pantsir-S1 air defense system is on the way to Syria.
By Leonidl (Own work) [CC BY-SA 3.0 or GFDL], via Wikimedia Commons
The entire system has yet to arrive but U.S. officials believe some control system components have been deployed at an airfield near Latakia.
While Syria already possess the Pantsir-S1, Western officials said the set arriving is a newer version.
It will be manned by Russian military, according to the Russian source.