A leading cleric who fled Syria has been chosen at a meeting in Qatar to head a new coalition to oppose President Bashar al-Assad's government.
Cleric Moaz al-Khatib, former Sunni Muslim imam of the Umayyad mosque in Damascus, is seen as a moderate.
Earlier, Syrian opposition groups agreed a deal to bring together their disparate factions.
The fractious opposition has been under pressure from the United States and other backers in the region to clinch a deal, the BBC reports.
Sheikh Moaz al-Khatib, 52, left Damascus for Cairo in July this year after several periods of detention by the Syrian authorities.
He had earlier attempted to bring the conflict to an end and in an interview with Reuters news agency in July said: "I want the Syrian people to remain as one hand."
In a speech in Doha in October he called for a political solution to save Syria from further destruction, arguing that negotiation would not "rescue the regime" but enable its departure with the least harm possible.
More than 36,000 people have been killed in the uprising against Mr Bashar's government that began in March 2011 and many more thousands more have fled the country.
On Saturday, the Israeli military said it had fired warning shots into Syria, after a mortar round from Syria hit an Israeli outpost in the occupied Golan Heights with no casualties.
It was the first time the two sides have exchanged fire since the 1973 Middle East war.