The Arab League won vital Syrian support on Monday (December 11) for its efforts to end a stand-off between Lebanon's pro-Western government and a Hezbollah-led opposition rallying hundreds of thousands in central Beirut, an envoy said. Arab League envoy Mustafa Osman Ismail said he also had agreement in principle from rival factions in Lebanon. Ismail arrived to Beirut on Monday for talks with Lebanese leaders. Arab League Secretary-General Amr Moussa would join him in the Lebanese capital on Tuesday (December 12). Syria's backing is seen as essential in forging any compromise in Lebanon. Although its troops left the country more than 18 months ago, Damascus still wields influence on many groups, the most powerful of which is the pro-Syrian Hezbollah. An anti-government protest campaign entered its 11th day on Monday with thousands of opposition supporters maintaining a round-the-clock vigil at a tent city in central Beirut. Hundreds of thousands of protesters attended a rally in Beirut on Sunday (December 10) to press demands for a national unity government that grants more power to Shi'ite Muslim Hezbollah and its Christian and Muslim allies. One security force source estimated the rally was the biggest in Lebanese history. Western-backed Prime Minister Fouad Siniora and his anti-Syrian allies have refused opposition demands, saying Hezbollah wanted to place Lebanon under the tutelage of Syria and Iran. Ismail had told Arabiya television that the proposals cover a unity government, passage of a U.N.-proposed international tribunal to try suspects in last year's killing of ex-premier Rafik al-Hariri and early presidential and general elections. Lebanese political sources said Ismail and Moussa would face a mountain to climb to get all parties not just to agree on the various issues but also on the sequence of implementing them. Pro-Syrian Hezbollah has charged that Siniora and some of his allies had tried to weaken the group during a 34-day war with Israel in July and August. Siniora has accused Hezbollah of trying to stage a coup following its war and commentators have warned the worsening stand-off could degenerate into sectarian violence in a country that is still trying to rebuild after a 1975-90 civil war. Whereas the last civil war started out primarily as a fight between Christian and Muslim militia, the main fault-line now lies between Lebanon's Sunni community and the Shi'ites. One Shi'ite protester has been killed and several people hurt in shooting incidents, riots and clashes between supporters of both sides over the past week.