Mining and smuggling is easy and cheap

An agreement may be ratified by the UN General Assembly by the end of the year but could still run into opposition in the United States, where there is concern about protectionism.

The Kimberley states hope to prevent international trading in diamonds which do not have a certificate of origin from their producer country, the BBC's Justin Pearce reports from Luanda.

Consequently, rebel groups will find it much harder to conduct illegal diamond trading.

A major fear for the industry is a consumer backlash if customers begin to associate diamonds with bloodshed in Africa, the world's poorest continent.

Protectionism fears

Angola's Deputy Minister of Mines, Antonio Sumbula, said the session had achieved its objectives and that final details of the certification scheme could be worked out at a meeting later in November in Botswana.

The Kimberley states also agreed on how to control the diamond trade within their own borders in order to give weight to an eventual international accord.

The question is whether this sets up a closed system and if a country which did not issue a certificate would not be able to import or export

US official

But not all participants shared Mr Sumbula's optimism that the process was on track since some countries still have unresolved concerns.

The United States, for one, is concerned that the certification scheme could clash with World Trade Organisation rules.

"The question is whether this sets up a closed system and if a country which did not issue a certificate would not be able to import or export," a US official told Reuters news agency.

The US imports about 10% of the global rough diamond trade and exports about a third of these.

In Angola itself diamonds have in the past been an important source of revenue to the UNITA rebel movement during decades of civil war.

Mr Sumbula admitted that a million dollars worth of diamonds were still exported illegally from Angola each day but he said the rebels no longer played a major part in this trade.