Chad is wracked by violence as President Idriss Deby struggles to hold onto power in the face of an alliance of rebel groups.

Fighting has escalated since the collapse of a short-lived October 2007 peace pact between the government and four rebel factions.

A February 2008 assault on the capital N'Djamena was the second rebel attack on the city in two years. The rebels, who call Deby's 19-year rule corrupt and dictatorial, warned the population to flee their homes, and thousands streamed across the river that marks the border with Cameroon.

Columns of Chadian rebels again advanced into Chad from the border area with Sudan in June 2008 and raided several towns.

Chad says Sudan is trying to overthrow Deby - whose health is bad - by backing Chadian rebels based in Sudan's Darfur region. Khartoum denies this and accuses Chad of aiding and abetting Darfur insurgents.

The fighting also threatens humanitarian operations supporting refugees and displaced civilians in Chad's east and south.

A European Union force was deployed early 2008 to protect aid operations in Chad and Central African Republic, and contain any spillover from the conflict in Darfur. In March 2009 it handed over its operations to a United Nations force.

Experts fear the instability in Chad may lead to all-out war with Sudan, giving Khartoum an excuse to crack down on Darfur rebels who are sympathetic to Deby.

Deby seized power in a Libyan and Sudanese-backed coup in 1990 and went on to win the country's first two multi-party presidential elections in 1996 and in 2001, which critics say were rigged.

His opponents say Deby favours members of his own Zaghawa clan, who account for less then 3 percent of the population.

Deby changed the constitution in 2005 to allow him to stand for a third term, prompting a wave of desertions from the army.

In April 2006, government forces repelled an attack on the capital staged by the rebel group United Front for Change (FUC), under the leadership of Mahamat Nour Abdelkerim.

The following month, Deby held presidential elections, which were boycotted by opposition parties. Deby won, but his former supporters in the army continued to switch to rebel factions.

A rebel coalition carried out another assault on the capital in February 2008, which was swiftly followed by a threat to attack the southern oil-producing Doba region unless Deby agreed to talks with his opponents. Another attack from Darfur-based rebels in June 2008 was contained before it reached N'Djamena.

The coalition included the three main Chadian rebel groups: the United Force for Democracy and Development (UFDD), the Rally for Forces for Change (RFC), and UFDD-Fondamentale, a splinter group of UFDD.

The largest rebel group is the UFDD, led by Mahamat Nouri. Nouri is a former member of Deby's government and was working as ambassador to Saudi Arabia when he defected two years ago. His forces are largely drawn from Nouri's Gorane ethnic group - the same clan as Chad's former President Hissene Habre, whom Deby ousted 19 years ago.

Another key group is the RFC, led by Deby's former chief of staff and cousin from his Zaghawa clan, Timan Erdimi.

The UFDD-Fondamentale is headed by Abdelwahid Aboud.

In January 2009 the rebels announced they had formed a new alliance called the Union of Resistance Forces, headed by Erdimi and made up of the UFDD, RFC, UFDD-Fondamentale and several other rebel groups.

Tensions between Deby and Sudan grew when Darfur rebels began organising on a large scale in 2002. Many of their fighters were from Deby's Zaghawa clan, and he came under increasing pressure to support them. Sudan responded by backing Chadian rebels in 2005. Many Chadian insurgents are based in Darfur, and Darfur insurgents in Chad.

Regional expert Alex De Waal says Darfuri rebel group Justice and Equality Movement helped Deby repel Chad rebel attacks on the capital.

Both governments deny any involvement in the rebel groups.

Arabs of Chadian origin have joined Janjaweed militia - armed Arab groups accused of atrocities in Darfur - and are thought to exercise significant influence on Janjaweed cross-border raids into eastern Chad. Some Janjaweed attacks seem to be coordinated with those of Chadian rebels. Human Rights Watch says others are backed by Sudan with helicopter gunships and Sudanese soldiers.

The rebels' stated aim is to oust Deby, but local analysts believe some want to win concessions from the government regarding Chad's newfound oil wealth. Exploitation of the country's massive oil reserves began in the southern Doba region in June 2000.

De Waal says Chad's conflict is part of a regional competition for dominance through a vast arc of central Africa that includes Central African Republic and Democratic Republic of Congo. He says Sudan, Libya, Uganda, Congo, Rwanda and even Eritrea are vying for influence across this area.

In response to the region's growing instability, in September 2007 the U.N. Security Council authorised a protection force for Chad and Central African Republic aimed at stemming the violence and preventing the possible spread of the Darfur conflict.

The European force (EUFOR) numbered over 3,000 troops in eastern Chad and northern Central African Republic. It was the European bloc's largest mission in Africa.

Former colonial power France initially proposed the mission and promised to provide roughly half the troops needed. Prior to EUFOR, France had installed a small force of 1,200 troops and six Mirage fighter jets under a bilateral defence accord to assist Deby.

Just days before EUFOR's deployment in early 2008, rebels attacked the capital. Some analysts say this is partly because they viewed the force as military protection for Deby because of its French links.

EUFOR handed over its operations to U.N. peacekeepers in March 2009. The U.N. force has a maximum capacity of 5,200 troops - including about 2,000 EU soldiers - and 300 police.

The contingent is intended to complement a bigger U.N./African Union peacekeeping force in Darfur, where political and ethnic conflict triggered by a rebellion has killed at least 200,000 people since 2003, according to the United Nations.

U.N. agencies and international relief groups are providing aid to around 265,000 refugees from Darfur and 180,000 displaced Chadians in the east, close to the Sudanese border.

Another 56,000 or so refugees who have fled insurgency and lawlessness in northwest Central African Republic are sheltering in camps in southern Chad.

Most Sudanese refugees live in camps in the semi-desert east, and depend on the U.N. World Food Programme (WFP) for food. They compete with locals for scarce water supplies and firewood.

Displaced Chadians also face shortages of food, water, shelter and adequate sanitation. Their situation gets worse during the annual "hunger gap" before the September harvest. They have been attacked when trying to return home to plant crops or collect food.

Agencies delivering aid have to contend with extremely poor infrastructure, including roads that become impassable during rainy seasons.

Outbreaks of fighting, looting and armed attacks on aid convoys have regularly forced temporary suspensions of aid activities in eastern Chad. As well as banditry, battles between rebels and the army have boosted insecurity around the eastern towns of Abeche, Adre and Guereda, which are important hubs for aid workers helping hundreds of thousands of refugees there.

Armed Arab Janjaweed militias based in Darfur stage cross-border raids into Chad, attacking Sudanese refugees and Chadian villagers from the Masalit and Dajo ethnic groups.

Relief groups worry that escalating violence could threaten the entire international aid operation in Chad. And the United Nations recorded over 150 attacks on foreign aid workers in 2008 alone.

Chad's government has several times called on the international community to remove the refugees and threatened to expel them itself, saying it cannot provide security for the refugees and aid agencies and that the refugee presence is creating tensions with Sudan.

Throughout Chad, access to health care is minimal. Around a fifth of children die before they reach the age of five, according to the U.N. Children's Fund.

International aid agencies found their reputation knocked by a 2007 adoption scandal, in which a small French charity called Zoe's Ark was intercepted and accused of trying to kidnap 103 children from Chad. Zoe's Ark said it wanted to place orphaned Darfuri children in foster care with French families, but many of the children were found to be from Chad and had parents who were still alive.

The case caused a diplomatic wrangle with France, where a court sentenced six of the charity's workers to eight years in prison. And it sparked widespread anger in Chad, with hundreds staging protests in the eastern town of Abeche. Deby pardoned the six in March 2008.