Cape Town — South Africa's President Kgalema Motlanthe has announced that the national flag will be flown at half-mast on Sunday to celebrate the life of Helen Suzman, an old opponent of the ruling African National Congress (ANC).

Suzman, who won international renown for her lone stand against apartheid in the apartheid parliament but who opposed the ANC's armed struggle and advocacy of economic sanctions, died on New Year's Day at the age of 91.

Motlanthe said South Africans of all persuasions should celebrate Suzman's life. He added: "At a time when the apartheid government sought a blackout on critical and independent views about the inhumanities inflicted on millions of South Africans, it was Helen Suzman who stood out as one of the few remaining voices of reason in the darkest days of our country's history."

Figures ranging from former President Nelson Mandela to Mosiuoa Lekota, the leader of the Congress of the People -- which broke away from the ANC last year -- have put on record their gratitude to Suzman for her attempts to intervene with apartheid authorities to ameliorate their conditions.

"Those of us who spent years of imprisonment on Robben Island will always remember with gratitude Helen's dispersed visits to the island to inspect the conditions under which we were kept," Lekota said in a statement.

Desmond Tutu, Archbishop Emeritus of Cape Town, said Suzman had "shone a light for justice and accountability" through her parliamentary opposition to apartheid.

In the early years of Tutu's leadership of the South African Council of Churches, he regularly asked her to intervene to alleviate cases of individual hardship, addressing her in correspondence as "My dear Child." At times Suzman, Tutu's senior in age by some years, signed off her replies as "The Dear Child."

In a tribute on Friday, Tutu said of her: "Through our country's darkest times she was an important reminder of the potential for a Rainbow Nation in which all South Africans could thrive together."