"International and regional smuggling networks have constructed elaborate covert operations to escape scrutiny," says the document.

"These networks are well connected to corrupt government officials worldwide. Companies and individuals are paid for their services either with raw diamonds or earnings from diamond sales."

Diamonds are the single most important reason for Savimbi's survival as a guerrilla fighter. Today, a similar mineral war is engulfing Congo, a country the size of western Europe which has eight per cent of the world's diamond reserves.

The Congo war has sucked in Rwanda, Uganda and Burundi on the side of the rebel forces; the Angolan, Zimbabwean and Namibian armies have backed Laurent Kabila, president of Congo.

The new development in the Congo conflict is that, for the first time, a diamond mining company has entered into commercial agreements with countries participating in the conflict.

In May it emerged that Oryx, a Cayman Islands registered mining company, had concluded a profit-sharing agreement with the Congolese and Zimbabwean governments for a $1bn diamond concession. The company, which sought a listing on the London stock market, insisted there was nothing unusual about the arrangement.

But the deal aroused controversy because the Zimbabwean army is providing security around the concession in the Kasai region, Congo's main source of industrial quality diamonds. Senior Zimbabwean army officers are on the board of a company that formed a joint venture with Oryx to exploit the concession.

Last month, the London stock exchange expressed concerns at Oryx's plans. The British government also criticised Oryx, and claimed the concession was in a conflict zone - a claim denied by the company. Oryx's financial advisers subsequently withdrew, forcing the company to abandon its flotation.

Other countries have tended to turn a blind eye to conflict diamonds, and some dealers in the main trading centres have been willing to buy the stones for years.