JOHANNESBURG - South African state-owned logistics company Transnet said on Friday that Portia Derby would step down as its chief executive officer from Oct. 31.

Derby and her senior management team have been under pressure from miners, industry bodies and labour unions over the deteriorating performance of the freight rail utility.

Miners say Transnet's underformance has cost mineral exporters billions of rand in potential revenue.

Transnet, whose flagship freight rail service has struggled due to the shortage of locomotives and spares as well as cable theft and vandalism of its infrastructure, slumped to a 5.7 billion rand ($302 million) loss in the year ended March 31.

Michelle Phillips, currently chief executive of Transnet Pipelines, will assume the role of acting CEO after Derby steps down, Transnet said.

Transnet also announced the resignation of its Chief Financial Officer (CFO) Nonkululeko Dlamini, with Hlengiwe Makhathini appointed as the acting CFO.

South African telecoms company Telkom said in a separate statement that it had appointed Dlamini as its CFO.

(Reporting by Amna Karimi in Bengaluru, Bhargav Acharya in Johannesburg and Nelson Banya in Harare; Editing by Alexander Winning)