Source: BBCNews
The US is intensifying diplomatic efforts to end the "hell" of Syria's civil war even as it increases support for moderate rebels, US Secretary of State John Kerry has said.
Mr Kerry is travelling to Vienna for talks with foreign ministers on ending the four-and-a-half year conflict.
Iran is for the first time taking part in such talks, which will also include Russia, Saudi Arabia and Turkey.
Russia and Iran both support Syrian President Bashar al-Assad.
The US, Turkey, Saudi Arabia and other Gulf Arab nations insist he cannot play any long-term role in the country's future.
Foreign ministers from the UK, France, Germany, Egypt, Lebanon and the EU have also confirmed they will attend the meeting, and other Middle Eastern powers are also expected.
"The challenge that we face in Syria today is nothing less than to chart a course out of hell," Mr Kerry said in a speech at the Carnegie Endowment for International Peace think-tank in Washington DC.
"While finding a way forward on Syria will not be easy... it is the most promising opportunity for a political opening we have seen."
He added: "At the end of the day, nothing would do more to bolster the fight against Daesh [the Islamic State militant group] than a political transition that sidelines Assad so that we can unite more of the country against extremism."
But in his speech, Mr Kerry stressed that the US and Russia also shared "common ground", arguing that both want "a united, secular Syria".