Tehran: Iran said it will take part for the first time in international talks aimed at resolving the brutal war in Syria, as a diplomatic push to end the conflict gained momentum.
Iran's Foreign Minister Javad Zarif will join key players in the Syria crisis -- including Russia, the United States and Saudi Arabia -- in Vienna on Friday for a renewed effort to end more than four years of bloodshed.
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 was to 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.
Washington is at loggerheads with Moscow over Syria, accusing Russian forces of concentrating their air campaign there on moderate opposition groups opposed to Syrian President Bashar al-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.
The inclusion of Iran -- a key ally of 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.
"We have reviewed the invitation, and it was decided that the foreign minister would attend the talks," Iranian foreign ministry spokeswoman Marzieh Afkham said.
It will be the first time all the major international players in the conflict are in the same room, but there has been no mention of either the Syrian government or the opposition attending.