Addis Ababa says it has defeated the Ogaden National Liberation Front (ONLF) guerrillas, which for years have fought for greater autonomy for the Ogaden region in Ethiopia's Somali state. But the rebels still carry out sporadic attacks on the military, which maintains a tight grip over the impoverished area.

The Ogaden region is near Ethiopia's border with Somalia and home to the Ogaden Somali sub-clan who are seen as the bedrock of support to the ONLF.

Restrictions on both the media and aid workers means it is difficult to establish the number and situation of people forced to leave their homes by the conflict but many analysts say hundreds of thousands of people are displaced, the Internal Displacement Monitoring Centre (IDMC) said in September 2009.

The government launched a major crackdown after ONLF rebels killed 74 people in an attack on a Chinese run oil exploration field in April 2007. The military blocked all circulation of goods and people to and from Degehabur, Qorahe, Wardheer, Fiq and Godey zones, making it difficult for the ONLF to resupply but also hurting the local economy.

Communities were forcibly relocated to areas controlled by the army - often villagers and nomads were given a few days' notice to move to larger villages and towns, says IDMC. Ethiopian soldiers destroyed property, confiscated livestock and burnt harvests, sometimes firing on and killing fleeing civilians, according to a 2007 Human Rights Watch report.

Food prices soared and this, combined with drought, triggered a humanitarian crisis in mid-2007. The U.N. was allowed to expand its activities in November 2007 and a dozen NGOs began humanitarian work, but security officials closely monitored and restricted their operations.

The army systematically coerced local communities to form militias to fight the ONLF - many clan leaders and civil servants who failed to recruit militias or support the counter-insurgency unconditionally have been arrested or dismissed, says the Brussels-based think tank International Crisis Group.

But abuses appear to have been carried out on both sides of the conflict. There have been reports of the ONLF punishing civilians who fail to provide food or shelter, and in 2007 ONLF fighters were accused of attacking large gatherings in towns, killing and wounding dozens.

Only a small number of aid agencies operate in Ogaden, and their activities are restricted by the army. Access is patchy, with groups suspending work at short notice.

Ogaden forms part of Ethiopia's Somali state which is one of the country's most underdeveloped regions, partly because of its remoteness, harsh climate, lack of infrastructure and chronic instability. Until Chinese engineers started moving into the region in late 2006, it could only boast just over 30 km (20 miles) of tarmac road, all around the regional capital Jijiga.

Battered by severe droughts and floods, the region carries out most of its trade with Somaliland, Somalia and the Middle East rather than "highland" Ethiopia.

The mainly Muslim and Somali speaking region obtained self-administration in 1993, when it was renamed the Somali Regional State. Its population size is highly disputed, and there have been allegations that the 1994 census findings were reduced from as much as 9.2 million or 7.5 million to 3.4 million, says the UK-based think tank Chatham House.

Western and Asian companies compete for exploration rights to the region's large oil and natural gas reserves.

Formed in 1984, many of the ONLF's members had supported Somalia in a failed war with Ethiopia over the region in the 1970s. The group's aims have varied over time from outright independence to joining a "greater Somalia" or gaining greater autonomy within Ethiopia.

The ONLF was created as a political party and for a while formed part of the regional government. It left in 1994 over a dispute over demands for a referendum on independence.

By mid-2009, its leadership and organisation was in disarray, with most of its leaders in exile in the UK and U.S., leaving field commanders in charge.

ONLF fighters take advantage of their close ties to the area’s largely nomadic communities, crossing expanses of open land to ambush the Ethiopian military convoys. They often melt into villages and hide among herders when counter-attacks are threatened.

When Addis Ababa sent troops into Somalia in December 2006 to help oust the Union of Islamic Courts insurgency group which had taken control of the capital Mogadishu, Ogaden became a battlefront between Ethiopian forces and Somali insurgents on both sides of the border. This triggered a wave of anti-Ethiopian feeling in Ogaden and boosted support for the ONLF, says ICG. Some Islamist fighters may have fled to Ogaden after they were ousted from Mogadishu.

Experts say the ONLF was active in Mogadishu in 2006 when it was controlled by the Union of Islamic Courts. But the ONLF is said to be mainly secular and the Islamist links are seen more as a marriage of convenience. The rebels deny having an Islamist agenda and say they no longer want to join a greater Somalia.

However some of the extremist Islamists now threatening to topple the government in Somalia want to create a "Greater Somalia" incorporating the Somali state. Some analysts say Ethiopian troops are back in Somalia to ensure they do not come to power, the Christian Science Monitor reported in May 2009. The Ethiopian government denies its troops are in Somalia.

The ONLF has received support from Ethiopia's rival Eritrea which helped build its military capacity in late 2006, says ICG.

The Oromo Liberation Front (OLF) operates in southern Ethiopia and northern Kenya and says it is fighting for the right to self determination for the Oromo people, who make up over a third of Ethiopia's 85 million population. It was formed in 1973 as a political party, and took up arms against the Ethiopian army in the early 1990s. The government's counter-insurgency activities in the region of Oromiya have caused displacement, but government restrictions mean little is known about their impact on civilians.

Ethiopia is also wracked by conflicts based on disputes over scarce water and pasture and administrative boundaries. In September 2009, there were conflicts in at least five of Ethiopia's nine regions, says the IDMC. In February 2009 alone, some 160,000 people were driven from their homes by conflict between the Garre of the Somali region and the Boran of the Oromiya region over a contested piece of land.