By Tiisetso Motsoeneng and Zandi Shabalala
JOHANNESBURG (Reuters) - South African President Jacob Zuma's son said on Friday he would sell his investments in a mining firm owned by friends of his father amid speculation that the wealthy family is wielding undue political influence.
Duduzane Zuma's announcement came days after First National Bank, a unit of FirstRand, joined three other South African companies in quitting as bankers and auditors of companies owned by the Indian-born Gupta family.
In a memo to staff seen by Reuters, Oakbay Investments - a holding company for Gupta businesses in South Africa - said it had approached government departments including Zuma's office to express "deep disappointment" over decisions by banks to close its accounts.
The Presidency and Oakbay did not immediately respond to requests for comment on the content of the memo.
Citing "aspersions" against his own family, Duduzane said he would also step down as a director of Shiva Uranium, the main subsidiary of Oakbay Resources, which houses the Gupta family's mining assets.
"I have decided to relinquish all positions that I hold at Oakbay companies and am exiting investments to preserve the jobs of Oakbay's thousands of employees and to de-politicise my participation in business," he said.
The mine is 26 percent-owned by Islandsite 255, a company of which Duduzane is also a director. It employs 648 people, the family said last month.
Last month deputy finance minister Mcebisi Jonas said the Guptas offered him the position of finance minister shortly before Zuma sacked then finance minister Nhlanhla Nene, in December, a move that sent markets into a tail-spin.
Zuma has denied suggestions the Guptas wield undue political power. The Guptas have also dismissed such reports, saying they are pawns in a political plot to get Zuma out of office.
Oakbay Resources said in a statement that chairman Atul Gupta and chief executive Varun Gupta had resigned with immediate effect. "This decision follows a sustained political attack on the company," it said in a statement.
The firm said it had created 3,500 jobs in South Africa's mining sector.
"SMOKE AND MIRRORS"
Oakbay Resources' statement did not say if the resigning members of the Gupta family would reduce their shareholdings in the company.
South Africa's elite police investigating unit, the Hawks, said last month it had launched a corruption probe into Duduzane and the Gupta family.
South Africa's main opposition party, the Democratic Alliance (DA), dismissed the resignations of Duduzane and the Guptas as an "exercise in smoke and mirrors" to protect their assets and profits.
Citing association risk, the local unit of global auditing firm KPMG cut ties with Oakbay Resources last month. Other companies that have severed links are investment bank Sasfin and lender Barclays Africa.
Oakbay Resources said it was being serviced by an Asian bank that did not want to be named.
The three Gupta brothers moved to South Africa from India at the end of apartheid in the early 1990s and went on to build a business empire that stretches from technology to the media to mining.
Zuma survived an impeachment motion by the opposition on Tuesday thanks to his African National Congress party's majority in parliament.
(Additional reporting by Ed Cropley; editing by Andrew Roche)