Durban, South Africa (CNN) -- A major international environmental group is pulling out of the process to guarantee that diamonds do not come from conflict zones, saying the Kimberley Process had refused "to evolve and address the clear links between diamonds, violence and tyranny."
The campaign group, Global Witness, had been part of the process to certify that precious stones are not "blood diamonds" for nine years.
Mike Davis announced the Global Witness decision Monday.
"We don't take this decision lightly, but we feel that we've now have reached a juncture where by continuing to participate we are inadvertently lending legitimacy to a scheme which is really misleading people in the diamond trade," he said.
The decision follows the controversial sale of a batch of diamonds from the Marange diamond fields in Zimbabwe, some of which are owned by companies associated with President Robert Mugabe's Zanu-PF party.
Davis said the Mugabe government has to rely on diamond income because of the intense international pressure on it.
"Diamonds are an absolute godsend for them and a curse for the rest of Zimbabwe," he said.
The Kimberley Process was developed in 2000 when a group of diamond-producing countries met in Kimberley, South Africa, to combat the trade in conflict diamonds.
The group's efforts were supported by the United Nations, which in December of 2000, ratified a resolution in support of the group.
CNN's Joseph Netto contributed to this report.