Two Western officials and a Russian source have said that Russia is providing anti-aircraft missiles to Syria as a part of military support for embattled Syrian President Bashar al- Assad.
The system will be operated by Russian troops rather than Syrians according to the Western officials.
One of the sources, a Western diplomat, said, "This system is the advanced version used by Russia and it's meant to be operated by Russians in Syria."
The information was separately confirmed by US officials, Reuters reported. One of the US officials said the entire system had not arrived yet, but some of the system's components had been positioned at an airfield in Latakia, a coastal province that is one of Assad's strongholds.
This would not be the first time that Russia is sending military air systems to Syria. According to the Russian source which is close to the Russian navy, the SA-22 system, known as Pantsir-S1 had previously been sent to Syria in 2013.
"There are plans now to send a new set," the source said.
US officials say they believe that Russia is sending weapons to Syria but the Russian intentions are not clear.
The US has led an aerial campaign in Syria against ISIS since September 2014.
In a press conference Russian Foreign Minister Sergey Lavrov said that Russia is sending weapons to Syria to fight ISIS and it is sending experts to train the Syrian Army on using those weapons.
Lavrov spoke about the necessity of coordination with the US in order to avoid "unintended incidents" over Syria.
US President Barack Obama said on Friday that the Russian military involvement in Syria is a sign that Syrian President Bashar al-Assad is turning to Russian advisers for help because he is worried.
Moscow, Syria's ally since the Cold War, has a naval base stationed in the Syrian coastal city of Tartus and it is likely hoping to defend its presence there since it is the only Russian base in the Mediterranean.Things have come to a head this year in which Assad’s grip on power has been made more tenuous after the international shift against him.
The four-year-long civil war in Syria has claimed the lives of more than 30,000 people while half of its 22-million population are displaced either internally or externally.