Diamonds will be tracked from source to sale
The international group trying to stop the trafficking in "blood diamonds" has given countries until the end of July to join the effort or be excluded from the legal diamond trade.
Representatives from 70 countries meeting in Johannesburg agreed to set a deadline of 31 July for nations to sign up for the certification system known as the Kimberley Process.
This aims to track the gems from mine to shop window and so curb the illicit trade in diamonds which has helped to fund wars and political violence across Africa.
But pressure groups remain sceptical, arguing the system lacks independent scrutiny and contains loopholes which could allow terrorist groups to fund their activities through diamond smuggling.
Experts say an estimated 4% of the $8.9bn (£6bn) international diamond trade is illegal.
Over the past decade, proceeds from conflict diamonds has helped to fund civil wars in Angola, Sierra Leone, Congo and Liberia.
Dog without teeth
Any country failing to sign up for the certification system would face a trading ban from other participants, said Abbey Chikane, who chaired the three-day meeting.
Campaigners say diamond sales in Africa have funded civil wars
"The most effective sanction is total isolation from the diamond industry," he said.
Under the scheme, government agencies must issue internationally recognised certificates to confirm the origins of rough diamonds.
Campaigners welcomed the move but say the process is still " a dog without teeth".
"We are calling for a monitoring mechanism to be established whereby you have independent experts," said Corinna Gilfillan of Global Witness.
Her group has also published a 100-page report setting out evidence to support suspicions that Osama Bin Laden's al-Qaeda network has used the diamond business to pay its way.
However, Mr Chikane said no confirmation had been found to substantiate these allegations, Reuters reported
The conference delegates admit that the Kimberley Process has its problems with several countries still to impalement the necessary legislation to enforce it.
But the scheme received a boost last week when the US - where two-thirds of the world's diamonds are sold - passed a law passed authorising diamond certification.