Some U.S. intelligence analysts say that “Russia is preparing to insert combat aircraft into Syria”, possibly in order to launch airstrikes against the radical groups fighting against the Assad regime (which is an important regional ally of the Kremlin). We already know, the same open source is reporting, that “in a development that caught U.S. intelligence by surprise, Russia has set up an air traffic control tower and modular housing units for hundreds of personnel at an airfield near Syria’s Mediterranean port of Latikia”.
CNN is reporting, also on September 5, 2015, that “U.S. Secretary of State John Kerry called Russian Foreign Minister Sergei Lavrov on Saturday [September 5] to discuss reports of an imminent Russian military buildup in Syria, according to the State Department”. The same open source is reporting that U.S. officials think that any Russian military buidup in Syria “could further escalate the conflict, lead to greater loss of innocent life, increase refugee flows and risk confrontation with the anti-ISIS Coalition operating in Syria”. A CNN commentator says that Russians “could be taking [military] steps to secure their own position if the Assad government falls”.
Some extra details
Another open source says that “Flightradar24.com has also reportedly tracked several Russian Air Force Il-76 airlifters flying to and from Damascus, according to The Aviationist”, and also that “sightings of Russian infantry vehicles and military advisers in Syria has prompted rumors that Putin has already put boots on the ground and may be preparing a large-scale counterterrorism operation alongside Iranian proxy militias”.
On September 4, 2015, international media quoted president Putin saying “it’s premature to talk about” a direct Russian involvement in combat actions in Syria, against the ISIL, but the Russian leader also said that his country is “already giving Syria quite serious help with equipment and training soldiers, with our weapons”.
Most probably, the new Russian move is directly aimed (at least) at seriously strengthening Moscow’s geo-strategic influence in the Middle East, while attempting to limit, if possible, increased Western influence in the same area. For some decades, in the Cold War era, Syria has been, strategically speaking, one of the most important Soviet strategic assets in the Middle East.
 “Russia may insert combat aircraft into Syria creating uneasy airspace”, CBS News, September 5, 2015, at the Internet address http://www.cbsnews.com/videos/russia-may-insert-combat-aircraft-into-syria-creating-uneasy-air-space/
 Ralph ELLIS, “Kerry calls Russia about possible military buildup in Syria”, CNN, September 5, 2015, text available at the Internet address http://edition.cnn.com/2015/09/05/middleeast/syria-kerry-calls-russia/index.html?eref=edition
 Natasha BERTRAND, “Putin is upping the ante in Syria”, Business Insider / Yahoo! Finance, September 5, 2015, at the Internet address http://finance.yahoo.com/news/looks-putin-upping-ante-syria-184600784.html
 “Premature to talk about Russian military action against IS [Islamic State]: Putin”, Yahoo! News / AFP, September 4, 2015, at the Internet address http://news.yahoo.com/premature-talk-russian-military-action-against-putin-074920065.html