Khulani Qoma, a spokesman for Eskom board's, denied the allegation, saying it was "devoid of logic".

Glencore in 2015 placed its Optimum coal mine under protection from creditors and later sold it to South Africa's Tegeta Exploration and Resources, a firm controlled by the Gupta brothers, who deny allegations they wield excessive influence over President Jacob Zuma.

"They (Eskom's CEO and chairman) insisted that I must suspend all the Glencore mining licences," Ramatlhodi told local media, adding he declined to give in to the pressure.

(Reporting by TJ Strydom; Editing by James Macharia and Mark Potter)