FACTBOX: Main actors in Somalia's conflict

(Reuters) - Pro-government militiamen in southern Somalia have seized a second town from rebels as President Sheikh Sharif Ahmed's fragile administration seeks to crush the insurgents, witnesses said on Wednesday.

Here are the main actors in Somalia's war:

ISLAMIST GROUPS

* Hizbul Islam is an umbrella organization of four opposition groups led by hardline cleric Sheikh Hassan Dahir Aweys, who is an influential figure among Islamists. The group fights alongside al Shabaab in a bid to topple the Western-backed government.

* Al Shabaab is a hardline group fighting the government. It wants to drive foreign forces out of Somalia and impose a strict form of Islamic law throughout the country. It was created as the armed wing of the Islamic Courts Union that controlled Mogadishu and much of the south in 2006. The United States has placed al Shabaab on its terrorism list. Analysts say the group is the best-financed and militarily strongest of the insurgents. It controls large parts of the capital and southern Somalia.

* Ahlu Sunna Waljamaca is a moderate Islamist group aligned with the government. The group is led by Sufi clerics and has fought and successfully beaten back al Shabaab in parts of central and southern Somalia. Stung by some al Shabaab practices including the desecration of graves, it has vowed to oust the group from other areas. It says the Somali war is sponsored by al Qaeda and other forces, and has nothing to do with Islam.

GOVERNMENT:

* The government of President Sheikh Sharif Ahmed -- himself a moderate Islamist and former rebel -- controls only a few districts in central Somalia and some of the capital Mogadishu. It has been unable to defeat the insurgents, but has had limited success in enticing some rebel leaders away. The government suffers from internal divisions and the loyalty of some of its security forces is also in question. It is endeavoring to build a 20,000-strong force, but says it needs more money from international donors to achieve that.

FOREIGN ACTORS:

* Ethiopia entered neighboring Somalia in late 2006 to oust the Islamic Courts Union from the capital, occupying much of the south until early this year. Addis Ababa sees any groups who may stoke separatist tensions in its southern, Somali-dominated Ogaden region as a threat to its national security. In the mid-1990s, Ethiopia crushed the al-Itihaad al-Islaami group led by Aweys and other figures in the current insurgency. It says it reserves the right to intervene again if necessary.

* Eritrea has battled arch-enemy Ethiopia since the 1960s with a brief respite in the 1990s. The United Nations, Somali government and other groups accuse Asmara of sending weapons and providing training for Somali insurgents. Eritrea denies the accusations, saying that outside influence is what is causing Somalia's problems.

* The African Union sent a force, now more than 5,000-strong, to Mogadishu in March 2007. The Ugandan and Burundi peacekeepers control little beyond the airport, the port and the presidential palace. Opposition groups say the AU presence is a sticking point to joining talks with the government. The peacekeepers have been unable to stop the violence. The AU expects to boost troop levels to 6,000.