US first lady Michelle Obama kicks off her six-day visit to Southern Africa today.

The wife of President Barack Obama will visit Pretoria, Johannesburg and Cape Town, and the Botswana capital, Gaborone, in a tour that begins tonight and draws to a close on Sunday.

The statuesque first lady - who has worn clothes that have launched the careers of many a fashion designer - will be accompanied by her two daughters, Malia and Sasha, but not her husband, on a trip that the White House says will focus on "youth leadership, education, health and 'wellness'".

Obama will also be travelling with her mother, Marian Robinson, and two of her nephews.

She will visit several places that are symbols of the decades-long anti-apartheid struggle, according to the itinerary released by the White House.

After meeting Nompumelelo Ntuli-Zuma, the second wife of President Jacob Zuma, on Tuesday, Obama will visit the Nelson Mandela Foundation, in Johannesburg, and meet Graca Machel, the former Mozambican first lady, now the wife of former president Nelson Mandela.

No plans have been announced for a visit to Mandela, 92, who is in fragile health, but the White House has left open the possibility of a meeting.

"She will be paying tribute to Mandela's legacy throughout her visit.

"She would treasure any opportunity to interact with Mandela; it depends on his ability to receive visitors," said Ben Rhodes, a White House deputy national security adviser.

Rhodes said the anti-apartheid struggle was "an inspiration to both South Africans and people across the continent, and to many people across the United States".

He noted that Obama has spoken repeatedly about the anti-apartheid movement, which he has called his first political cause.

"There's obviously a deep connection the Obamas feel to the South African experience," Rhodes said.

On Wednesday, Obama will go to one of the central symbols in the anti-apartheid fight, the Regina Mundi church, in Soweto.

The church was a sanctuary for students during the uprising of June16 1976, when a 12-year-old schoolboy, Hector Pietersen, was killed.

The next day, Obama visits Cape Town and Robben Island, the prison at which Mandela was held for 18 of the 27 years he was jailed.

During her visit to the Mother City, Obama will meet retired archbishop Desmond Tutu, who received the Nobel Prize in 1984, 10 years before the fall of the apartheid regime.

Obama will round out her visit to southern Africa with a stop in Gaborone. The White House has praised Botswana for its "democratic stability".

"It's important to underscore that this trip by the first lady is very directly connected to the president's agenda in Africa and to the Obama administration's foreign policy for Africa," said Rhodes.