A three-day meeting designed to tighten controls on the trade in so-called "conflict diamonds" has ended in Johannesburg. Representatives from 70 countries focused on the implementation of what is known as the Kimberley Process Certification Scheme, named for the South African mining city where it was launched.

The Kimberley Process aims to eradicate trade in conflict diamonds, also known as blood diamonds, which are mined in war zones. Conflict diamond revenues are blamed for fueling conflicts in countries such as Sierra Leone, Angola, and the Democratic Republic of Congo.

The Kimberley Process agreement applies to countries that produce, process, sell and buy diamonds. They must all have legal measures in place that ban trading in rough diamonds without a certificate of origin.

The chairman of the Kimberley Process, Abbey Chikane, says participating countries have until the end of May to prove that they have passed those laws. He says he will issue a final list of participating countries by July 31st. Any country not on that list will be, in his words, marginalized and isolated from the Kimberley Process.

He says, "Effectively, what it means is that that particular country will not be able to trade with major diamond producing, processing, and exporting countries around the world. Which means it will not have access to large markets, such as the United States or Japan. It also will not have access to trading centers such as India, Israel, Belgium, et cetera."

Liberia has asked to have a monitoring team sent to the country so it can apply for membership in the Kimberley Process. Liberia was hoping that the monitors would help convince the United Nations to lift its ban on Liberian diamonds.

But Mr. Chikane says that as long as the United Nations embargo is in place, the group cannot send monitors to Liberia or take any other action toward legitimizing the Liberian diamond trade.

Activist groups such as Global Witness have led the campaign against conflict diamonds during the past few years. The activists have largely welcomed a decision to send a review team to the Central African Republic, to make sure the country is complying with the Kimberley Process after a recent coup.

But the activists are complaining that there are still too many loopholes in the process, which could too easily allow the trade in conflict diamonds to continue.

Global Witness campaigner Corinna Gilfillan says she was hoping the delegates would agree to include regular, independent monitoring missions for all member countries - similar to the special team that will be sent to the Central African Republic.

She says, "We do welcome the fact that there was some progress made on some key issues. However, one of our main concerns is there was no agreement to adopt a regular, independent monitoring mechanism into the Kimberley Process to ensure that it works and it's not open to abuse. As far as we're concerned, having a credible, regular monitoring mechanism is absolutely crucial to the credibility of the whole system, and to stopping the trade in conflict diamonds."

Activists say an independent monitoring program would keep countries from laundering conflict diamonds by claiming they come from their own diamond mines. They single out Zimbabwe and the Republic of Congo, both of which export large numbers of diamonds that analysts say were really mined in the Democratic Republic of Congo.

Mr. Chikane says such a monitoring program may eventually be necessary. And he concedes that right now, some countries do not appear to be complying with the Kimberley Process regulations, although he refused to name names.

But he says the current plan is for a system of peer review, requiring individual countries to report other members they suspect of breaking the rules.