Russia's actions in Syria are fuelling the country's war, which can only be ended with an unconditional exit of President Bashar Al-Assad, Saudi Foreign Minister Adel Al-Jubeir said ahead of a meeting with his US, Russian and Turkish counterparts.

"We believe that the Russian interference in Syria is very dangerous because it exacerbates the conflict," Al-Jubeir told reporters in Vienna, adding the Saudis had made this clear to the Russians.

Russia's air force has flown over 780 sorties against almost 800 targets in Syria since September 30.

"We believe that it will be viewed as Russia inserting itself in a sectarian conflict in the Middle East. We're concerned that this will trigger emotions in the Muslim world that will cause an increase in fighters to go to Syria."

Almost 80 percent of Russia's declared targets in Syria have been in areas not held by Islamic State, a Reuters analysis of Russian Defence Ministry data shows, undermining Moscow's assertions that its aim is to defeat the group.

When asked whether Assad could play a role in any Syrian interim government Al-Jubeir said: "His role would be to leave Syria... The best case scenario is that we wake up in the morning and Bashar Al-Assad is not there."

US State Secretary John Kerry is due to meet Al-Jubeir, Turkish Foreign Minister Feridun Sinirlioglu and Russian Foreign Minister Sergei Lavrov in Vienna on Friday to discuss Syria. - Reuters