A diamond mining firm jointly owned by China and Zimbabwe started auctioning diamonds after a ban was lifted by the Kimberley Process, state media reported on Tuesday.

The anouncement came a day after a campaign group that helped set up the global diamond watchdog pulled out of the Process over its removal of the ban.

"The response from buyers was pleasant," mines ministry secretary Prince Mupazviriwo is quoted as saying in the Herald newspaper, confirming that diamond miner Anjin is auctioning its diamond stock-piles.

"The buyers were from various countries in the world."

The Kimberley Process Certification Scheme (KPCS) in November allowed Zimbabwe to sell its gems again after a ban over alleged human rights abuses. This followed a conditional allowance to sell diamonds in June, a decision which divided the body already then.

Rights group Global Witness, which helped set up the voluntary certification scheme, on Monday said this decision was the final straw and pulled out of the body.

Investor interest was "a positive move especially after having complied with the KPCS requirements," said Mupazviriwo.

Officials close to the diamond sales could not give the value of the gems that were auctioned, The Herald said.

Anjin is sitting on an estimated two million carats of diamonds which were stockpiled during the ban.

It is one of three companies allowed to sell their diamonds again. It is unclear whether the other two, Marange Resources and Mbada mines, have restarted sales.

Human Rights Watch alleges that Mugabe's army killed more than 200 people two years after the 2006 discovery of the mines in an operation to clear small-scale miners from the area.

The government called "ridiculous" a BBC report in August exposing a camp run by Zimbabwean security forces where civilians were forced to dig for diamonds and tortured in the diamond-rich Marange area in the country's east.

Zimbabwe says it expects to rake $600 million in diamond sales in 2012.