FACTBOX: Who is attending Darfur talks and who is not

(Reuters) - Delegations from Darfur rebel groups, Sudanese government negotiators and international mediators gathered in Sirte, Libya on Saturday for peace talks aimed at ending 4-1/2 years of war in western Sudan.

The decision on the eve of the talks by two main Darfur rebel groups not to attend, however, cast doubt on the viability of the discussions.

Analysts say if the Libya talks lack support from key players any agreement coming out of them would likely suffer the same fate as a 2006 deal signed by only one Darfur faction. It did little, if anything, to end the violence.

Here are some details about the Darfur peace process and who may attend Saturday's talks:

* BACKGROUND:

-- Since the badly flawed 2006 Darfur Peace Agreement, signed by only one of three rebel negotiating groups, insurgents have split into more than a dozen factions, creating a chaotic security environment on the ground.

-- The first talks in Nigeria's capital Abuja were hindered not only by rebel divisions but by a disconnect between field commanders and the political leadership at the negotiating table.

-- The African Union-United Nations mediated talks in Sirte, Libya, to begin on Saturday, hoped to bring all those who have rejected last year's deal into the peace process.

* REBELS WHO WILL ATTEND PEACE TALKS:

-- JUSTICE AND EQUALITY MOVEMENT-COLLECTIVE LEADERSHIP: Led by Bahar Idriss Abu Garda, former vice chairman of Khalil Ibrahim's JEM. The group was formed in September after Ibrahim sacked Abu Garda and his ex-military chief Abdallah Abanda.

-- JEM-AZRAQ - Led by Idriss Ibrahim Azraq. Broke away from Khalil Ibrahim's JEM in 2007, accusing him of "ethnic chauvinism" and an inclination toward "Islamic fundamentalism".

-- REVOLUTIONARY DEMOCRATIC FORCES FRONT - Led by Salah Abu Surrah. An Arab-based Darfur rebel movement formed in 2006.

-- NATIONAL MOVEMENT FOR REFORM AND DEVELOPMENT - Led at the talks by Khalil Abdullah. It broke from JEM in 2004 and is said to have Chadian backing.

-- UNITED REVOLUTIONARY FORCE FRONT - Led at the talks by Alhadi Agabeldour. An Arab-led rebel group opposed to the government.

-- SUDAN LIBERATION MOVEMENT-G19 - Led at the talks by Khamees Abdullah. It is a small faction that rejected the 2006 Darfur agreement, and formed the military wing of the former National Redemption Front.

-- SUDAN FEDERAL DEMOCRATIC ALLIANCE - Led by Ahmed Ibrahim Diraige. The group, which rejected the Abuja peace deal, was part of the former National Redemption Front created in Eritrea in June 2006.