Johannesburg - Anglo-Dutch energy giant Shell was ordered on Wednesday to withdraw claims about controversial shale gas drilling in an advertisement carried in several South African newspapers.The Advertising Standards Authority (ASA) said the company had made claims that were unsubstantiated and likely to mislead, in a complaint brought by a lobby group that is fighting a bid by Shell to explore for gas deposits.Shell wants to drill using hydraulic fracturing known as "fracking" in the country's vast central Karoo region and published a full-page print advertisement in several daily and weeklies in April."We are disappointed by the ruling," said Bonang Mohale, Shell South Africa chairperson."The purpose of the advert was to provide information direct to the public to enable them to properly assess the nature of the proposed shale gas exploration in the Karoo, as well as the accompanying technology of hydraulic fracturing."The matter was brought by the Treasure the Karoo Action Group which welcomed the decision. The authority ruled in its favour on four counts, dismissed four complaints and withheld ruling on one matter.The findings against Shell included claims that fracking was used in 90% of natural gas wells and that there were no documented cases of groundwater contamination from the process."We do not know enough about the long-term or even the short-term damage fracking could inflict on the environment," said action group chairman Jonathan Deal."We should not be misled by the emotional calls and manufactured facts of such adverts."Shell is among several companies hoping to drill for potential gas trapped in the Karoo by pumping water, sand and chemicals deep underground at high pressure to force out deposits trapped in track.South Africa's government has halted all new applications and any decisions to explore for gas in the Karoo while it carries out a study after a massive public backlash against the "fracking" process over environmental fears.