Published: 04:01 EST, 30 October 2015 | Updated: 06:47 EST, 30 October 2015
Major powers, including arch-rivals Iran and Saudi Arabia, are meeting for the first time today in search of a political solution to end the devastating war in Syria.
Top diplomats from more than a dozen nations have gathered in Vienna to discuss the fate of President Bashar al-Assad, who has defied Western demands to step down.
In a sign of its growing diplomatic clout, Iran, a longtime sponsor of Assad's regime, is joining the talks for the first time, months after striking a landmark nuclear deal with world powers.
Top diplomats from more than a dozen nations have gathered in Vienna to narrow differences over the fate of President Bashar al-Assad, who has defied Western demands to step down
Talks are being held in Vienna with officials hoping to build up a peace deal to end the war in Syria
But there are no talk of representatives of the Syrian regime or the opposition attending the talks aimed at ending a four-year war that has claimed a quarter of a million lives.
In Washington, which along with its Arab and Turkish allies backs Syrian rebels, officials have expressed a cautious hope that the players would agree the outline of a transition that would eventually see Assad step aside.
US Secretary of State John Kerry, while warning against an immediate solution, hasvedescribed the talks as 'the most promising opportunity for a political opening we have seen'.
He met separately with Iran's Foreign Minister Mohammad Javad Zarif and Russia's Sergei Lavrov on the eve of Friday's meeting.
'Now it is the right time to bring Iran to the table,' Kerry said.
Later, Kerry and Lavrov were joined by foreign ministers Feridun Sinirlioglu of Turkey and Adel al-Jubeir of Saudi Arabia.
Horrific: Syrian boys receive treatment at a makeshift hospital following an airstrike in Douma
Horrific: The world powers will be hoping the meeting can put an end to the four-year war that has claimed a quarter of a million lives
There was no talk of representatives of the Assad regime or the opposition attending the talks
Devastating: Russian air strikes reportedly hit a market, killing 45 civilians in Douma, on the outskirts of Damascus
Long suffering: Many of the injured and dead are children, caught up in the bloody conflict
Russia, which has waged a month of intense air strikes against Assad's armed opponents, has also urged preparations for parliamentary and presidential elections in Syria.
But the idea has been rejected by rebels who say a vote would be impossible in the current circumstances, with millions of Syrians displaced, cities standing in ruins and two-thirds of the country in the hands of jihadists and other armed groups.
There are also doubts about whether Tehran and Moscow are ready to push Assad to step aside, particularly at a time when the Islamic State group is seeking to tighten its grip on swathes of the country for its self-proclaimed caliphate.
Even so, mounting international concerns about the outpouring of Syrian refugees and the growing jihadist threat could set the scene for some kind of political compromise, experts say.
'Overall, we have for the very first time around the table all the major actors and we have a situation of fatigue on the ground, so it could lead to a potential breakthrough,' said Karim Bitar of the Paris-based Institute for International and Strategic Relations.
Even getting Iran and Saudi Arabia -- the Middle East's foremost Shiite and Sunni powers which back opposing sides in conflicts across the Arab world -- to sit at the same table would mark progress.
Russia, which has waged a month of intense air strikes against Assad's armed opponents, has also urged preparations for parliamentary and presidential elections in Syria
Ready: US Secretary of State John Kerry (centre left) and Staffan de Mistura, (centre right) UN Special Envoy for Syria, take their seats for a meeting at Hotel Imperial
Farewell for now: US Secretary of State John Kerry leaves the Hotel Imperial in Vienna, Austria
Shocking: Russia has repeatedly carried out air strikes against US backed rebels in north-western Syria
Indiscriminate: Activists have accused the Russians of carrying out indiscriminate attacks on civilians
On Thursday the United States said that recent raids by Russia had 'caused collateral damage,' including at a hospital, which NGOs have reported but Moscow has denied
Jubeir, in an interview with the BBC, made it clear that Riyadh is sticking by its view that Assad must leave office quickly.
'He will go either through a political process or he will be removed by force,' he warned.
Russia and Iran have made it equally clear that Assad has a right to play a role in an eventual transition towards a mooted transitional unity government and later elections.
'Apparently those who have tried to solve the Syrian crisis reached the conclusion that without Iran's presence there will be no possibility of reaching a rational solution,' Zarif said, according to Iranian state news agency IRNA.
The West has accused Russia of concentrating its air campaign in Syria on moderate opposition groups opposed to Assad's rule, although Moscow says it is focusing on defeating the Islamic State group and other 'terrorist' organisations.
On Thursday the United States said that recent raids by Russia had 'caused collateral damage,' including at a hospital, which NGOs have reported but Moscow has denied.
Syrian conflict: The fighting has escalated in recent months since Russia intervened in the conflict
Last Thursday, Russia called reports of the strike on a clinic 'fake,' attacking the British-based Syrian Observatory for Human Rights for reporting the information
Smoke rises after the air crafts belonging to the Syrian army bombed opposition-controlled district of Ayn Tarma in Damascus two days ago
Trail of destruction: The bombed out remnants of the opposition controlled district of Ayn Tarma, Syria
'We've some information that would lead us to believe that Russian military aircraft did hit a hospital,' State Department spokesman John Kirby told reporters.
Last Thursday, Russia called reports of the strike on a clinic 'fake,' attacking the British-based Syrian Observatory for Human Rights for reporting the information.
The monitoring group said that 13 people including medical staff were killed in Russian air strikes on October 20 against a field hospital in the northwestern province of Idlib that was run by the Syrian-American Medical Society.
Iran and Lebanon's Shiite armed movement Hezbollah also have troops in Syria to advise or support Assad's forces.
Representatives from Britain, Egypt, France, Germany, Italy, Lebanon, the European Union and possibly other Arab states, were also expected to attend Friday's talks.