Correctional Services spokesman Manelisi Wolela has denied allegations that student leader Mcebo Dla.
The diamond market seemed to be shrugging off the consumer slowdown and the negative publicity caused by the Oscar-nominated film Blood Diamond last year, De Beers' interim results showed.
Despite supply constraints, a stronger price for rough diamonds resulted in underlying earnings in the six months to June 30 rising 5percent to $324million.
This means a $156million profit contribution to Anglo American, which holds a 45percent stake in the company.
The group said that while consumer demand was holding up, sales of unpolished stones were down 7percent to $3,4billion in the first half of the year due to difficulties in sourcing supplies.
De Beers is winding down a deal to buy diamonds from Russia's Alrosa after the European Commission last year raised concerns that the relationship would tighten the South African firm's grip on the market.