The Free Syrian Army has committed an affront to all humanity by kidnapping and threatening to execute a female Ukrainian journalist and announcing that they will kill all Russians and Ukrainians they find in Syria. This could be taken to be akin to a declaration of war, obviously the armed insurgents in Syria have been emboldened to a point that they have stepped into an area where they are beyond the law.
With the terrorists also threatening Russian and Ukrainian Diplomatic Missions this could set off a chain of events that may pull the Russian Federation directly into the conflict. If the lives of Russians are at risk Russia has the right to protect its citizens and to assist unaligned Ukraine if there is such a request.