FACTBOX: Syrian rebel groups

BEIRUT (Reuters) - A year and a half after an uprising against President Bashar al-Assad erupted and grew into an armed insurgency, many tens of thousands of fighters are battling the Syrian leader.
But they remain divided and their military campaigns have been largely uncoordinated. The latest efforts to unite Assad's foes will have to overcome geographical divisions, personal rivalries and political or religious rifts.
Below are the groups fighting in Syria.
1- FREE SYRIAN ARMY
*A rebel umbrella group of roughly 80,000 which started with army defectors who left in protest against killings of unarmed protesters.
*Leadership was based in neighbouring Turkey for one year and exerted little authority over fighters on the ground.
*Working to resolve differences between rival local commanders and unite in a joint command based in Syria.
Groups within the FSA:
- MILITARY COUNCILS
*Led by defected officers, the Military Councils are most powerful in Aleppo and Homs, but include brigades countrywide.
*The council in Aleppo, led by Colonel Abdel-Jabbar al-Oqaidi, includes the powerful Tawheed Brigade and smaller ones.
*The council in Homs province is led by Colonel Qassem Saadeddine.
*The council in the capital Damascus is weaker, and its leadership is challenged by two Islamist-leaning umbrella groups: Ansar al-Islam and the smaller Ahfad al-Rasool.
*At first, the heads of military councils reported to FSA leader Riad al-Asaad but criticised his long stay in Turkey. Asaad said the FSA leadership will now move to northern Syria.
- REVOLUTIONARY MILITARY COUNCILS
*Made up largely of civilians who were initially calling for peaceful revolt against Assad but armed themselves in response to his heavy crackdown and now fight under the FSA banner.
*Many of the newly-formed units around the country are small and work locally - rebels say most of the brigades are made up of around 30 fighters.
- FRONT TO LIBERATE SYRIA
*A group of Syrian Islamist brigades who joined forces last month in an attempt to unite the rebels.
*The Front is believed to be composed of 40,000 members.
*Led by the head of the Sokour al-Sham Brigade of Idlib, Ahmad al-Sheikh, the units operate mainly in Damascus, Aleppo, Idlib and Homs.
*Does not acknowledge Asaad as the leader of the FSA but works with FSA units.
*Includes the prominent Farooq Brigade, which is linked to the Muslim Brotherhood and mainly operates in Homs province.
2 - OTHER GROUPS OUTSIDE FSA
*Independent groups are also operating. The main ones are the Nusra Front, an al Qaeda affiliate, and the Umma Brigade.
*When the Nusra Front came to prominence with a series of bombings in Damascus and Aleppo, some Syrian activists at first denied its existence and blamed the attacks on the government.
*Sustained attacks and a strong presence on the battlefield make it a serious force in the conflict. Some rebels reject the group for its radical interpretation of Islam and for bomb attacks on security targets that have also killed civilians, like a recent Aleppo bomb which killed 48 people.
*The number of Nusra Front fighters is unknown. It sometimes works alongside other brigades when attacking army bases.
*The Umma Brigade - named after the global community of Muslims - is led by Libyan veteran fighter Mahdi al-Harati, who left last year with 20 of his top men to train Syrian rebels.
*Its powerhouse is in Idlib province and is composed of 6,000 fighters, mostly Syrians.
*Free Syrian Army rebels say there are also other groups operating on their own, and that some are involved in looting and kidnap for ransom.
3 - FOREIGN FIGHTERS
*Independent foreign fighters, driven by scenes of massacres on television, have come to Syria to fight against Assad.
*They include Chechens, Yemenis, Afghans, Jordanians, Iraqis, Gulf Arabs and Westerners.
*Some work alone and others in coordination with Syrian rebel groups.
(Reporting by Mariam Karouny; editing by Mark Heinrich)