The conflict, with its roots in the Cold War, is erupting again and already 250,000 people have fled their homes.

The BBC's Anna Richardson reports on Angola - The Forgotten Vietnam

For 15 years, the ruling MPLA enjoyed backing from Soviet Union money and 30,000 Cuban troops. The Unita rebels had US support and South African soldiers.

Hundreds of thousands were maimed or killed and the fighting continued even after the Cold War ended.

Now, war is looming again and it is being fuelled by wealth that could be going into rebuilding the shattered country.

Oil boom is funding government troops

Angola is in the middle of an oil boom and has some of the best diamond fields in the world.

But riches from these lucrative industries are going into the pockets of the two warring sides.

For 20 years, Angolan President Jose Eduardo dos Santos has controlled the oil fields. It has given his loyal supporters a luxurious lifestyle. It has also fuelled his war machine.

And with new oil fields being found at a faster rate off Angola's Atlantic coast he shows no sign of running out of cash.

Angola currently produces $10bn of oil each day - a figure that is expected to treble in the decade - and multinational oil companies are offering hundreds of millions of dollars to explore virgin areas of the seabed.

Diamonds are a rebel's best friend

For the rebels diamonds are the answer to any funding problems.

Divers pick diamonds from crocodile infetsed rivers

Angola's interior has some of the best diamond fields in the world - 80% are of the highest gem quality - and they can be extracted by divers and simple equipment.

From 1992-1997, Unita ran the world's biggest diamond smuggling operation - using the proceeds to buy arms.

Despite United Nations sanctions imposed on Unita earlier this year the human rights group, Global Witness says international diamond dealers are continuing to trade with the rebels.

Some of the diamond fields have been handed back to the government under the UN peace treaty.

But they are again becoming crucial to Unita and the rebels killed 11 workers in a raid on the Yetwene mine last November.

UN despair

As all-out war looms people are on the move.

The UN estimates that this year there has been 250,000 new Angolan refugees.

Some have walked up to 200km from areas closed to foreign observers to reach refugee camps.

Now, after two UN planes were shot down, allegedly by Unita, the UN says it is withdrawing 1,000 observers from areas of combat. And a complete pull out has not been discounted.