The new chief of the UN-sponsored Kimberley Process that aims to stop "blood diamonds" reaching market said she was in talks to regain support of a campaign group that recently quit the scheme.

Kimberley Process chairwoman Gillian Milovanovic on Friday said she was "continuing discussions" with London-based Global Witness, which helped set up the voluntary certification scheme in 2003, about their complaints.

Global Witness pulled out of the scheme in December, citing a recent decision to allow Zimbabwe to sell gems tainted by army killings as the final straw.

"We are sorry (Global Witness) made the decision" to withdraw, Milovanovic, the former US ambassador to Mali who was appointed to her new post last month, told reporters during a teleconference.

"We are in constant touch. We will continue to be speaking with one another gathering ideas, conversing so that it is not the end of the discussion," she added.

Seventy-five countries and several human rights groups joined the Kimberley Process after a report to the United Nations revealed that diamond mining funded wars in Sierra Leone and Liberia and human rights abuses against miners in other countries.

Participating countries agreed not to allow diamonds lacking Kimberley Process certification to be imported or exported, in a bid to cut the links between diamond sales that have funded human killings during war and conflict.

Global Witness was one of the first human rights and environmental groups to reveal the blood diamond abuses.

But the organization withdrew its participation on December 5 after claiming it was ineffective in preventing torture and other abuses of miners in the Ivory Coast, Venezuela and Zimbabwe.

"Nearly nine years after the Kimberley Process was launched, the sad truth is that most consumers still cannot be sure where their diamonds come from, nor whether they are financing armed violence or abusive regimes," said Global Witness, explaining its criticism.

The group described a Kimberley Process authorization granted to Zimbabwe in June to sell diamonds from mines where the country's army is accused of abuses as "an outrage."

Despite Global Witness's decision, Milovanovic said that the certification scheme "has clearly had a positive effect on stemming the tide of conflict diamonds and that the trend definitely has been a positive one."