Russian military jets have carried out air strikes in Syria for the first time, targeting what Moscow said were Isis positions.
The strikes were launched hours after the Russian parliament gave their seal of approval on Wednesday morning.
However, a US official has cast doubt on the claim that the Kremlin is tragetting Isis, saying the Russians appeared to be attacking opposition groups fighting Syrian government forces.
And on the ground, video footage has emerged of Russian planes flying over anti-Assad rebel groups in Hama.
President Vladimir Putin sought to portray the airstrikes as a pre-emptive attack against the Islamic militants who have taken over large parts of Syria and Iraq.
Here’s what we know about why Russia would want to target Isis groups:
1. Why has Russia moved now?
Isis holds more than 50 per cent of Syria according to the Syrian Observatory for Human Rights and has been advancing towards a strategically important road linking Damascus to the north. Its forces are now only 22 miles from this highway and President Assad’s army is on the retreat after four years of war and heavy casualties.
Russia’s key aim, therefore, is to prevent collapse – unlikely – or the significant weakening of the Assad regime. The US is not bombing Isis in Syria in areas the jihadist group is fighting the Syrian army.
Russia has also decided to move now following the failure of Mr Putin to reach any agreement with the US at the UN General Assembly meeting in New York where the threat of Isis has been high on the agenda.
2. What is Russia’s plan – to defeat Isis or save Assad?
Their priority is to defeat Isis and then save the Assad regime in Damascus. Despite all the controversy over whether Assad should stay or go, the war would carry on in either case. This is very much a civil war with committed supporters on either side. In the short term Russia wants to stop Isis, and if possible defeat it – though this not likely to happen.
3. Is this a proxy war between Russia and the US?
No - they are both on same side against Isis and al-Qaeda clones. They are wholly divided, however, on how power should be shared in a post-Isis Syria, so there is a rivalry there.
4. How might Obama respond?
It is difficult for Obama to have any influence since he has a complete vacuum of policy in Syria. In theory he wishes to contain and defeat the so-called “Islamic State” (Isis) but has failed to do either. The Russians have now filled that vacuum but with uncertain long-term results.