HARARE (Reuters) - Zimbabwe has banned all diamond exports, including from a unit of Rio Tinto, until gemstones from its controversial Marange fields are certified by the Kimberley Process, state media said on Thursday 27 May.

"I have suspended all diamond exports from Zimbabwe with immediate effect until the issue of the KPCS has been sorted out," Obert Mpofu, the mines minister told the state-owned Herald newspaper.

Zimbabwe is yet to get a nod from the Kimberley Process Certification Scheme, which regulates the global diamond trade, to sell diamonds from Marange. The government accuses the West of a plot to stop Zimbabwe from benefitting from the resource.

Rights groups, which accuse Zimbabwe's security forces of widespread atrocities in a bid to stop thousands of illegal miners in the poorly secured fields in the eastern part of the country, have been pushing for a ban on the diamonds.

But diamond exports from Rio Tinto's Murowa mine, which produced 124,000 carats last year, and privately owned River Ranch, have continued.

State media reported on Thursday 27 May that Mpofu said Murowa and River Ranch would also be affected by the ban.

Rio Tinto and the minister were not immediately available for comment.

The ban could be a move by the government to put pressure on the Kimberley Process to allow the Marange diamonds to be exported.

Two little known South African companies, Grandwell Holdings and Core Mining are mining diamonds in a 50:50 joint venture with the government in Marange and authorities say they have since the start of the year stockpiled more than 2 million carats awaiting Kimberley Process certification for export.

A monitor from the international industry regulator is in the country to investigate whether Zimbabwe has complied with

Kimberley Process recommendations and may announce on Friday 28 May whether the country can start diamond exports from Marange.

"There seems to be a belief among our detractors that in Zimbabwe there are some diamonds which are pure or more acceptable to them than others," Mpofu said. "Can such a situation be allowed to continue?"

A leading Israeli diamond official told Reuters last week that monitoring Zimbabwe diamond sales will be the focus of a meeting of the Kimberley Process in Tel Aviv next month.