"The Russians are no longer just advisors," a Lebanese source told Reuters. 

"The Russians have decided to join the war against terrorism."

Russia's increased military involvement in Syria has US officials concerned and outright skeptical over Russian President Vladimir Putin's intentions.

Putin has said that Russia wants to "create some kind of an international coalition to fight terrorism and extremism."

The US State Department isn't buying it.

"Russia is not a member of the coalition against ISIL, and what we've said is that their continued support to the Assad regime has actually fostered the growth of ISIL inside Syria and made the situation worse," State Department spokesman John Kirby said on Wednesday, using an acronym for the Islamic State (aka ISIS and Daesh).