New measures aimed at curbing the trade in conflict diamonds have been criticised by non-governmental organisations (NGOs).
The Kimberley Process covers the trade in uncut diamonds
Representatives of more than 60 countries and leaders of the diamond industry have agreed to introduce a system where individual countries volunteer for their diamond trading activities to be independently monitored
But the NGO's say the system is not tight enough to stop trade in the so-called "blood diamonds".
"No agreement is credible without a mandatory monitoring system and the Kimberley Process is no exception," said Bethan Brookes from Action Aid.
"This is a loophole through which conflict diamonds can slip," she said.
The Kimberley Process was set up to curb the flood of diamonds out of countries such as the Democratic Republic of Congo and Liberia, the proceeds of which perpetuated the bloodshed there.
Nevertheless the BBC's Hilary Andersson in Johannesburg says the agreement reached in the South African resort of Sun City is still a breakthrough in the fight against the trade in illegal diamonds.
According to the agreement those diamond producing countries can request independent monitoring visits.
The Congo and the Democratic Republic of the Congo, both countries with huge trades in diamonds, have agreed to request such visits.
The idea is that these visits might give countries with bad records a clean bill of health that will help promote the legal diamond industry.
The agreement is a watered-down version of a proposal to introduce forced monitoring of countries under suspicion.
A system put in place in February already requires that rough diamonds must have a certificate confirming their country of origin.
Blood diamonds have helped fund the activities of the Angolan Unita movement and of the RUF in Sierra Leone, a rebel group accused of horrific atrocities.
Zimbabwe's government is also suspected of enriching top officials through the illegal diamond trade.