Energy and petrochemicals giant Shell has expressed concern about the slow progress South Africa is making in granting licenses for shale gas exploration, despite having accepted bids six years ago.

Shell is one of several firms seeking to explore the semi-desert Karoo region, near South Africa's border with Namibia, which is believed to have one of the largest untapped shale deposits worldwide.

South Africa lifted its 18-month moratorium on hydraulic fracturing, or fracking, to weigh environmental and economic implications in September 2012, but companies wanting to drill argue that nothing has happened since.

Environmental groups have vehemently opposed drilling for shale gas in the Karoo, arguing that it may contaminate underground water supply - reasons similar to those Germany is leveraging to restrict fracking on its soil.

Shell said earlier that, if allowed to drill, it would spend $200 million on the first exploration phase of six wells.