A boy walks amid damaged buildings in the town of Douma, eastern Ghouta in Damascus.

U.S. Secretary of State John Kerry warned on Wednesday that this week’s international talks on the war in Syria will not find an immediate political solution but nevertheless represent 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,” he said in a speech on Middle East policy just before he was to set off for Vienna.

“My friends, the challenge that we face in Syria today is nothing less than to chart a course out of hell.”

Kerry was to meet with his counterparts from a dozen world powers in the Austrian capital for a series of bilateral and multilateral talks on Thursday and Friday to find consensus on a political way forward in Syria.

Speaking to the Carnegie Endowment for International Peace, Kerry noted that Syrian President Bashar al-Assad’s ally Iran is to take part for the first time, along with Damascus’ other main military backer Russia.

Washington is at loggerheads with Moscow over its stance, accusing Russian forces of concentrating their air campaign on moderate opposition groups opposed to Assad’s rule rather than on the Islamic State of Iraq and Syria group.

“But it is also clear that Russia and the United States share an amazing amount of common ground on this,” he said, arguing that both want “a united, secular Syria” in which citizens can choose their own leader through elections.

“We agree that all of these steps can only be achieved, and Syria can only be saved, through a political settlement,” he said, arguing that “one man” — Assad — cannot be allowed to stand in the way of peace.

Two previous rounds of talks on Syria — dubbed Geneva I and Geneva II, in June 2012 and January-February 2014 — agreed on the principle of forming an interim unity government and sidelining Assad.

But Assad, with support from Iran, Russia and the Lebanese Shiite movement Hezbollah, has clung on, while the United States and its Arab and Turkish allies have continued to support and arm mainly Sunni rebels.

“Ultimately, to defeat Daesh, we have to end the war in Syria, and that is America’s goal,” Kerry said, using a term for the ISIS based on its Arabic acronym.

The Vienna discussions are expected to be the first time all major international players in the conflict, linked to the nearly five-year war, will participate.

Saudi Arabia and other U.S. allies in the Middle East had previously opposed the involvement of Iran, which they blame for fomenting unrest in several parts of the Middle East, including Syria, Yemen and Iraq.

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