The latest escalation in fighting in Syria has heightened international involvement and threatens to bring the conflict from proxy to all-out war.
On Tuesday, Turkey raised further objections to Russia's incursions into its airspace, following Russian bombing of targets in Syria. While Russia maintains it is targeting Islamic State (IS), the jihadi terrorist group which has made significant incursions in Syria, Western powers claim it is also firing on Western-backed Syrian opposition groups and civilians.
Here, we take a look at the main divisions over what should be done in Syria.
The U.S. has led criticism of Russian actions in Syria and a coalition of forces trying to halt the spread of IS in Syria. President Barack Obama has been criticized for not doing more, but the Pentagon seems to be trying to avoid supporting anti-IS forces who are still Islamist, in what is an extremely complicated situation.
Russia's President Vladimir Putin appears to have scored a diplomatic victory, at home at least, by taking a more active part in the Syrian conflict on the side of long-term ally and former President Bashar al-Assad.
Russian volunteers who have fought in Ukraine are likely to travel to Syria to back Assad-led forces, according to Admiral Vladimir Komoyedov, the head of the Russian parliament's defense committee. This at least suggests that Russia is not yet at the stage of committing ground forces to the war, which could raise the specter of the long and painful Afghanistan war of the 1980s. However, it is a way of suggesting to the West that the possibility is there if they do not come forward with some form of alliance.
At the heart of this conflict is the sectarian division in the Middle East between the two most popular branches of Islam, Sunni and Shia, and the two best-known regimes associated with them, Saudi Arabia and Iran.
Saudi Arabia and Qatar are both opposed to IS and the Assad regime, led by Alawite (Shia) Muslims, and are part of the U.S.-led coalition opposing IS. However, some Sunni Arab states have also helped support other non-IS Islamist extremists within Syria.
Syria itself has no oil worth speaking of, but it is surely no coincidence that the Russian intervention comes after its economy has been near-crippled by Saudi Arabia-led OPEC maintaining previous levels of oil production despite the collapsing oil price. What the Russian economy needs is a recovery in the price of oil, its main export, and fast, which is more likely to happen when the Middle East is in conflict.