Russia's deployment of war planes, missile systems, tanks, and armoured troop carriers has dramatically changed the shape of the conflict on the ground in Syria and stepped up political pressure on western and Arab governments to come to terms with president Bashar al-Assad.
Russia's airstrikes have altered the situation because they have been against sites where Syrian military forces are under pressure from anti-regime insurgents linked to or co-operating with al-Qaeda affiliate Jabhat al-Nusra, or locations hosting concentrations of Russian rebel Chechen fighters.
This strategic targeting shows Moscow gives priority to strengthening Damascus against near enemies rather than striking Islamic State.
Furthermore, by hitting Nusra and its allies, which have the support of Turkey, Saudi Arabia and Qatar, Russia has made it clear al-Qaeda is not off-limits and cannot be considered part of the "moderate" camp.
US air cover
Russia’s deployment also appears to have precipitated the announcement of US plans to provide air cover for an offensive by Syrian Kurdish and Arab ground forces against IS headquarters in the Syrian city of Raqqa and to seal a 96km stretch on Syria’s border with Turkey through which IS receives recruits, arms, funds and goods.
The revelation came after former army chief Gen Martin Dempsey admitted the 14-month-old US air campaign was "tactically stalemated". The inclusion of Syrian Kurds means they will have to be armed in spite of opposition from Ankara.
Russia’s intervention effectively puts an end to Turkey’s demand – resisted by the US – for the creation of a no-fly zone and safe haven in northern Syria where insurgents could be based and refugees accommodated.
Finally, Moscow has upgraded weapons provided and stepped up deliveries to the Syrian army, which has been struggling to contain IS and other fundamentalist factions since March. This was when the Saudis and Qataris boosted weapons supplies to Nusra and IS, enabling the former to seize control of the northwestern province of Idlib and the latter to capture Palmyra.
Russia's involvement coincides with shifts in the positions of key Arab and western governments. The hardliners in the anti-Assad camp are Turkey, Saudi Arabia, Qatar, France, the expatriate National Coalition and insurgent groups.
Last week, however, following a meeting in Moscow with Russia's president Vladimir Putin, his Turkish counterpart Recep Tayyip Erdogan conceded Assad could be involved in transition negotiations. This was later dismissed by prime minister Ahmet Davutoglu, architect of Turkey's increasingly unpopular anti-Assad campaign launched in 2011.
Under pressure to end the Syrian war in light of the refugee crisis in Europe, the US, UK and other European countries have moved from the hardline camp. The US and Britain contend Assad cannot "be part of Syria's future" but may not have to step down before talks on a transition begin.
Germany's chancellor Angela Merkel calls for talks with "many actors", including Assad, the US, Russia, Iran and Saudi Arabia. This places Germany between the weakening US/UK and the pro-Assad camp which consists of Russia, Iran, Lebanon's Hizbullah, Iraq and Egypt. Last week Iraq formed a joint command centre with Russia, Syria and Iran to share data on IS.