The Hefer commission was set up by President Mbeki

Bulelani Ngcuka, told the Hefer Commission of inquiry in Johannesburg that allegations against him were designed to discredit his office.

The probe into past activities of Mr Ngcuka was set up last September, after the governing African National Congress said he had been a spy in the 1980s.

Judge Joos Hefer is to deliver his findings before the end of the year.

'Corrupt'

"I'm here today because the organisation I've been tasked to lead has performed its functions without fear, without favour and without prejudice. I'm here to make it clear that we shall not be intimidated by those who have sought to discredit us in an attempt to derail our investigations in order to protect their own vested interests," Mr Ngcuka told the Hefer commission.

BULELANI NGCUKA Unknown in 1994 Pledged to fight corruption Secured conviction of Winnie Mandela Accused of spying for apartheid Full profile

The BBC's Carolyn Dempster in Johannesburg says this is the final chapter in a messy political saga to determine whether or not he was ever a spy for the apartheid government

Mr Ngcuka's two main accusers are former Transport Minister Mac Maharaj and former ANC intelligence agent Mo Shaik.

Mr Maharaj is currently under investigation by the elite Scorpions police unit on suspicion of being linked with a corrupt deal when he was a minister.

And Mo Shaik's brother, Shabir Shaik is facing charges of corruption linked to the government's controversial arms procurement deal.