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Feb 8 (Reuters) - The European Union may send peacekeepers to eastern Chad next week to protect more than half a million refugees and civilians from violence spilling over the border from Sudan's war-torn Darfur.

The deployment, temporarily postponed after a rebel attack on Chad's capital last weekend, involves some soldiers going to northeast Central African Republic, where fighting between rebel groups and government soldiers has displaced thousands.

Here is some background on the instability in Chad, Sudan and Central African Republic, neighbours in the heart of Africa.

KEY FACTS:

* CHAD - Still one of the world's poorest countries, Chad began producing oil in 2003 with the completion of a $3.7 billion pipeline operated by a U.S.-led consortium which links oilfields to terminals on Cameroon's Atlantic coast.

* SUDAN - At 2.5 million sq km (967,500 sq miles), Sudan is Africa's largest country, straddling the middle reaches of the Nile. Oil was a catalyst in its long, bitter north-south war.

* CENTRAL AFRICAN REPUBLIC - Central African Republic is also among the world's poorest, despite having diamonds and other minerals. Its 4 million people have a life expectancy of 39 years and average annual income of $350, World Bank data show.

CONFLICT:

* CHAD - A lightning assault on N'Djamena in April 2006 was launched from the east by rebels in an unsuccessful bid to overthrow President Idriss Deby, who went on to win an election.

In the first few days of February 2008, rebels again fought their way into N'Djamena, besieging Deby in his presidential palace. After heavy fighting, in which aid workers estimate at least 160 people were killed and up to 850 more were injured, they pulled back east from the Chadian capital. Deby's government said it beat them back.

Chad's former colonial ruler France, which has warplanes and more than 1,000 troops stationed in the country, obtained a United Nations Security Council declaration in support of Deby and said it could intervene more directly to help him in Chad.

* SUDAN - Darfur rebels took up arms in 2003, saying the government discriminated against mostly non-Arabs there. Experts estimate 200,000 people have been killed and some 2.5 million have fled their homes in almost five years of revolt. Khartoum says only 9,000 have died.

The United Nations and the African Union are due to deploy a 26,000-strong peacekeeping force in Darfur.

* CENTRAL AFRICAN REPUBLIC - The country has had 11 mutinies or attempted coups in the past decade. President Francois Bozize, a former army general, seized power in a coup in 2003 before legitimising his presidency through a 2005 election. The United Nations estimates nearly 300,000 people have been forced from their homes since violence began in 2005.

CROSS-BORDER TENSIONS:

-- Around 50,000 refugees from fighting in Central African Republic are sheltering in southern Chad.

-- French special forces intervened in late 2006 to dislodge rebels who had seized a swathe of northeastern Central African Republic around the town of Birao. The fighting marked a spillover south of the Darfur conflict.

-- Relations between Sudan and Chad have been tense in recent years as both try to quell insurgencies on either side of their frontier. They accuse each other of backing rebels trying to overthrow their respective governments.

-- Eastern Chad has seen a spillover of refugees and Arab Janjaweed raiders from Darfur. Khartoum has routinely rejected Chadian accusations that it supports Chadian rebels fighting the insurgency against Deby.

-- The recent conflict in Chad has delayed the deployment of a 3,700-strong EU peacekeeping force to the east of the country. EU officials say they hope the deployment can resume next week. (Writing by David Cutler, London Editorial Reference Unit and Pascal Fletcher in Dakar; editing by Philippa Fletcher)

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