JOHANNESBURG - A major human rights watchdog on Monday left the international body charged with keeping "blood diamonds" off the market, accusing the regulatory group of refusing to address links between the gems, violence, and tyranny.

Global Witness' departure from the Kimberley Process raises questions about whether consumers can be sure the diamonds they buy aren't fueling conflict.

In a statement, Global Witness cited what it called Kimberley Process' failures in Ivory Coast, Venezuela, and Zimbabwe.

"Consumers have a right to know what they're buying, and what was done to obtain it," said Charmian Gooch, a Global Witness founding director. "The diamond industry must finally take responsibility for its supply chains and prove that the stones it sells are clean."

The diamond industry, rights groups, and 75 countries have worked together as members of the Kimberley Process since 2003 to impose requirements on its members to enable them to certify rough diamonds as "conflict-free" so that purchasers can be confident they are not funding violence. The project was born after wars in Sierra Leone and Liberia that were fueled by "blood diamonds."

Partnership-Africa Canada, the other major rights group in the process, said it shared the frustrations of Global Witness, but would remain in the regulatory group in hopes of helping it reform. Alan Martin, Partnership-Africa Canada's research director, said his group would look again in a year at whether to remain.

"The Kimberley Process is a necessary but insufficient tool," Martin said.

Alfred Brownell, a Liberian human rights lawyer who closely follows the Kimberley Process, said that among the reforms he would like to see is a broader definition of conflict diamonds. Diamonds do not have to fuel war to be bloody, he said, citing allegations of human rights violations in mining in Zimbabwe.

Like Martin, Brownell said he respected Global Witness's decision, but still had hope the Kimberley Process could be fixed.