MELBOURNE (REUTERS) - Rio Tinto chairman Jan du Plessis is set to step down and take up the chairmanship of BT Group, with the announcement to be made by Britain's top mobile and broadband operator on Thursday, the Financial Times reported.

Rio Tinto, the world no 2 miner, declined to comment on the report.

Du Plessis, chairman since 2009, has led Rio Tinto through a volatile period, as it scrambled to pay down US$39 billion (S$55.29 billion) in debt from its Alcan takeover, scrapped a controversial tie-up with China's Chinalco, sacked a chief executive after over-priced acquisitions and fended off a bid from Glencore .

He would be leaving just as the company faces investigations in Australia, the United Kingdom and United States over an alleged bribe in 2010 tied to a massive iron ore project in Guinea, expected to take years to resolve.

Du Plessis, 63, was also until last year the chairman of SABMiller, which was taken over by Anheuser-Busch InBev in one of the largest corporate mergers in history.