BEIRUT - Syria's divided rebels have agreed to set up a joint leadership to oversee their battle to overthrow President Bashar Assad after coming under pressure from their foreign supporters to unite, two rebel sources said on Tuesday.The decision, taken by dozens of rebels including Free Syrian Army leaders at a meeting inside Syria on Sunday, aims to improve military coordination among fighters and create a single leadership which they hope outside powers would be prepared to arm with more powerful weapons.Mistrust and differences over leadership, tactics and sources of funding have widened rifts between largely autonomous brigades scattered across Syria.The rebel sources said pressure increased on their leaders to unite as the unrest threatened to spill over into neighboring countries."There will never be a unity inside Syria unless the countries supporting the revolt agree because each group is supported and backed by a country," one rebel source said."Now the countries are becoming nervous and the Syrian issue has become bigger than they expected and almost out of control."The leadership is expected to be composed of 60 members who will represent most of the forces fighting in Syria, including the Islamic rebel group the Liberation Front."The agreement has been reached, they only need to sign it," one rebel source said. The foreign backers "are telling us: 'Sort yourselves out and unite, we need a clear and credible side to provide it with quality weapons'." He said Qatar and Turkey were the main forces behind the agreement.It is the latest attempt to bring together Assad's disparate armed opponents, most of whom have been fighting nominally under the FSA's banner but in practice have operated independently.The new leadership will include FSA leaders Riad al-Asaad and Mustafa Sheikh - criticized by many rebels because they were based in Turkey - and recently defected General Mohammad Haj Ali, as well as heads of rebel provincial military councils inside Syria like Qassem Saadeddine, based in Homs province.The 19-month-old revolt started as peaceful protests and turned into a civil war, with the mainly Sunni rebels fighting to overthrow Assad, from the Alawite minority. It is also attracting foreign Sunni jihadis, alarming Western powers and some regional states.