John Kerry and Sergey Lavrov meet in Vienna on Friday as they were due to hold talks on the Syrian conflict with their counterparts from Turkey and Saudi Arabia.

AFP/Vienna

Russia's Foreign Minister Sergei Lavrov held talks on the war in Syria with US counterpart John Kerry on Friday after Moscow thrust itself into the heart of the crisis with its bombing campaign backing President Bashar al-Assad.

Lavrov shook hands with Kerry as they sat down at a Vienna hotel for a crunch meeting that will then see the duo joined by Saudi Foreign Minister Adel al-Jubeir and Turkey's Feridun Sinirlioglu.

Washington, Riyadh and Ankara - which all back groups battling against Assad - are looking to sound out Lavrov after the embattled Syrian strongman made a surprise visit to Moscow to meet President Vladimir Putin this week.

On September 30 Russia launched a bombing campaign in Syria, which has shifted the dynamics of the brutal four-and-a-half year war - allowing Assad's battle-weary forces to go on the offensive and overshadowing a US-led coalition bombing the Islamic State (IS) group.

The US and its regional allies have decried Russia's strikes, insisting Moscow is not focusing on IS as it claims, but other groups fighting the regime in Damascus, and that the Kremlin's intervention will only prolong the bloodshed.

Assad's fate  

Assad's fate remains a major stumbling block for talks and after years of failure to stop the bloodshed in Syria there was scant hope of any major breakthrough in Vienna.

His surprise visit to Moscow on Tuesday - his first known trip abroad since the start of the Syrian conflict in 2011 - has now placed the Kremlin as the key link to the strongman.

Washington and its regional allies have long insisted Assad has to go for there to be any chance of a political solution to fighting that has cost more than 250,000 lives, but Moscow says it must first help him defeat IS and other "terrorists" before talks can start on any reforms.

"The aim of the US is to get rid of Assad, probably that is so, our aim is to defeat terrorism, to battle terror, and to help President Assad claim victory over terror," Putin said on Thursday in the Black Sea resort of Sochi.

"In this way, we can then create the conditions for the start and, I hope the successful reaching of a conclusion, of the political process to find a settlement."

Meanwhile, Kerry said in Berlin that while all sides agreed on the need to find a political solution and battle IS only "one thing stands in the way... a person called Assad - Bashar al-Assad".

Diplomatic blitz

However, analysts say some Assad opponents appear to be softening their line and conceding that he could remain in power temporarily, while Moscow does not seem wedded to the strongman long-term.

Putin - who has been isolated by the West for some 15 months over the Ukraine crisis - went on a diplomatic blitz in the wake of the visit by Moscow's long-standing ally, calling the leaders of Saudi Arabia, Turkey, Jordan and Egypt.

Russia has been frantically trying to get the US and its coalition partners to cooperate with its bombing campaign in Syria, and Putin on Thursday stressed the need for "joint work" to defeat "terrorism" in Syria.

Moscow had called for other Middle East powers - particularly staunch Assad ally Iran, which is also backing his forces on the ground - to take part in the Syria talks but that was rejected due mainly to strong Saudi opposition.

Lavrov is also expected to meet his counterpart from Jordan Nasser Judeh separately in the Austrian capital to discuss the situation in Syria, Russia's foreign ministry said.