Iran says won't accept pressures for Assad's ouster

Speaking after meeting Mr Zarif, the EU's foreign policy chief Federica Mogherini said the Vienna talks would bring together "all the relevant actors playing around the same table, trying to define a common space for the beginning of a political process".

Any peace plan for Syria allowing President Bashar al-Assad to stand in early elections after a transition period would be "mad" because he is the root of the problem and holding a nationwide poll is impossible, a Syrian opposition figure said. One of the key issues might be discussed is the future of Syrian President Bashar al-Assad.

Since the civil war began in 2011, half of the Syrian population has been displaced and an estimated 300,000 have died.

Russian Federation has said representatives of Iraq and Lebanon will participate in the ministerial talks on Syria in a broader format in Vienna on Friday.

Still absent, however, is anyone from inside Syria, as neither the Assad government nor the rebels appear to have sent representatives or even been invited.

Kerry has warned that this week's talks may not secure an immediate political solution but nevertheless represent the best and probably only hope available.

Iranian deputy foreign minister Amir Abdollahian, who will be attending the talks, was quoted by the country's media as saying the country "does not insist on keeping Assad in power forever".

Russia, the United States, Saudi Arabia and Turkey, the four major powers meeting in Vienna, support opposite sides in a war that USA secretary of state John Kerry has described as "hell".

"Russia's entrance, given its potential and capabilities, is something we see is going to have an effect on limiting terrorism in Syria and eradicating it", Egyptian Foreign Minister Sameh Shoukry said.

That no one from the Syrian opposition or government will attend highlights the fact that Syria is spiraling ever deeper into proxy war.

U.S. and European officials voiced scepticism, however, about the possibility of a breakthrough at Friday's conference, which was expected to include foreign ministers and senior officials from 17 countries.

Earlier, French Foreign Minister Laurent Fabius said France and its allies had agreed on the need for a "precise timetable" for Assad's departure.

Later, Kerry and Lavrov were joined by foreign ministers Feridun Sinirlioglu of Turkey and Adel al-Jubeir of Saudi Arabia.

Iran has shown no signs it is ready to dump Assad.

Tehran has emerged as a staunch regional ally of the Assad government in Syria's long-lasting conflict.

Saudi Arabia, which has demanded Assad's eventual removal as a "bottom line" and has continued to support favoured rebel groups with arms and funding, said the talks' success would depend on whether Russian Federation and Iran were "serious" about finding a solution. "I think if Iran is accepting the dialogue, to now sit next to the worldwide community, to find a way out of the Syrian crisis by dialogue and politics, I think it's because it doesn't want to lose any more commanders".

In sitting down to negotiate with Iran and Russian Federation, the U.S.is recognizing their increasingly powerful presence in Syria, as Russian Federation pounds opposition fighters with airstrikes and Iran sends troops as reinforcements.