South Africa's main opposition party has announced anti-apartheid activist Mamphela Ramphele will be its presidential candidate this year.

Ms Ramphele, the companion of late black consciousness leader Steve Biko, only formed her Agang party last year.

Democratic Alliance leader Helen Zille said "there was no better person" than Ms Ramphele to lead their election bid.

Analysts say the move is intended to ward off accusations that the DA is "too white" to win power.

The two leaders said they were joining forces to bring unity to South Africa - the "unity Madiba [Nelson Mandela] fought for".

Ms Ramphele, 66, is seen as an impressive figure with impeccable "struggle credentials" - factors which still influence the way some South Africans vote.

However, her Agang party has failed to make much of an impact since its launch last year. It is bankrupt and a month ago was unable to pay its staff.

The BBC's Milton Nkosi in Johannesburg says the DA takeover of Agang will certainly make this year's election more interesting but the governing African National Congress (ANC) is still expected to retain its majority.

He says Jacob Zuma is likely to still be president after the elections, regardless of the long list of corruption scandals that are dogging his administration.

The elections are due in April and will mark the 20th anniversary of the elections which saw the ANC come to power, ending decades of white minority rule.

As a community doctor who worked in the Eastern Cape alongside her partner, the late Steve Biko, Ms Ramphele led grassroots resistance against white minority rule in the 1970s.

She went on to become a director of the World Bank, a vice-chancellor at the University of Cape Town, and until recently sat on the board of a major mining company.