CAPE TOWN, Nov 19 (Reuters) - South African power utility Eskom is facing deliberate acts of sabotage by unknown criminals, its chief executive said on Friday, as he showed images of a high capacity electricity pylon toppled when all eight of its metal support stays were cut. Struggling under a mountain of debt, state-owned Eskom regularly implements power outages that have unnerved investors and cost Africa"s most industrialised economy billions of dollars in lost output. Claims of sabotage at Eskom"s fleet of ageing coal-fired power plants supplying the bulk of South Africa"s electricity, and which are prone to mechanical breakdowns, have swirled around for years, but CEO Andre de Ruyter"s comments on Friday were the firmest yet from a senior executive. "The evidence does appear to be, at least prima facie, incontrovertible that there is malice afoot and that we need to take action," he said during a media briefing. Discovered on Wednesday evening, the toppled pylon which showed no signs of metal fatigue or corrosion, is found along the main distribution lines feeding coal conveyor belts at the 3,708 megawatt (MW) Lethabo plant in the Free State province. "What further arouses suspicion that this was a deliberate act of sabotage is that nothing was stolen from the site ... so this was not an economic crime," he said. Quick action by Eskom prevented Lethabo power station from running out of coal, a prospect which could have worsened power cuts to Stage 6, when around 6,000 MW is shed from the national grid, versus Eskom"s nominal installed capacity of 46,000 MW. De Ruyter did not speculate on the motives behind the attacks, which come amid mounting criticism of Eskom management"s inability to stop power cuts. He said Eskom was using infrared-equipped drones to help patrol strategic infrastructure but it was virtually impossible to safeguard some 390,000 kms (242,335 miles) of transmission and distribution lines. Reporting by Wendell Roelf; Editing by Emelia Sithole-Matarise Our Standards: The Thomson Reuters Trust Principles.