By Dave Clark
Key players in the diplomatic push to end the Syrian war are meeting in Vienna, seeking common ground over a political transition, ahead of Iran's first-time appearance at international talks on the conflict.
Top diplomats from Russia, the United States, Saudi Arabia and Turkey will hold the second round of talks on Syria in less than a week, ahead of the larger meeting of regional players, including Iran, on Friday (local time).
Iran's Foreign Minister Mohammad Javad Zarif will join representatives from Britain, Egypt, France, Germany, Italy, Lebanon and the European Union as the international community seeks to end more than four years of bloodshed.
It will be the first time all the major players in the conflict are in the same room, though there has been no mention of either the Syrian government or the opposition attending.
The inclusion of Iran, a key backer of Syrian President Bashar al-Assad, in this week's meetings marks a crucial shift after Tehran was excluded from earlier talks, mainly because of opposition from Washington and Riyadh.
US Secretary of State John Kerry cautioned that this week's talks would not secure an immediate political solution, but nevertheless represented the best hope available.
"While finding a way forward on Syria will not be easy – it's not going to be automatic – it is the most promising opportunity for a political opening we have seen," Kerry said just before he set off for Vienna.
"The challenge that we face in Syria today is nothing less than to chart a course out of hell," he added.
Britain's Foreign Office said the United Arab Emirates, Qatar and Jordan will also attend the meeting on Friday.
Washington is at loggerheads with Moscow over Syria, accusing Russian forces of concentrating their air campaign there on moderate opposition groups opposed to Assad's rule.
Moscow says its bombing campaign is targeting Islamic State jihadists and also other "terrorist" groups.
But Kerry stressed that the US and Russia also shared "common ground", arguing that both want "a united, secular Syria" in which citizens can choose their own leader through elections.
After months of failure, efforts to find a breakthrough have gained pace as hundreds of thousands of Syrians have fled their shattered country.
Serious divisions remain over when or whether Assad should step down, and four-way Russia-US-Saudi-Turkey talks in Vienna last Friday failed to make a breakthrough.
On one side, Russia and Iran are backing Assad's forces on the ground and say Damascus must be helped to defeat "terrorism" before a political process can take shape.
On the other, the United States and its key regional allies Turkey and Saudi Arabia are supporting groups fighting Assad and insist he must go.
Meanwhile, the Pentagon announced plans to step up attacks on Islamic State jihadists in Syria and Iraq, with Defence Secretary Ashton Carter saying he expected more air strikes and even possible "direct action on the ground".