WASHINGTON - US first lady Michelle Obama left for Africa on Sunday, embarking on her second official solo journey abroad with a goal of advancing US policies on education, health, and democracy.

The first lady will arrive on Monday in South Africa, where she will make stops in Johannesburg and Cape Town. Later in the week she will visit Botswana.

Photo taken on June 15, 2011 shows US First Lady Michelle Obama (C) joins volunteers to build a playground at Imagine Southeast Public Charter School in Washington. [Photo/Agencies]

Her trip will be rich with imagery.

As the wife of the first black US president, Mrs. Obama's travel on the continent adds a different symbolic heft than previous first ladies' trips there have had.

In South Africa she will meet Graca Machel, the wife of former South African President Nelson Mandela. She will also visit the island where Mandela was imprisoned under apartheid.

In Botswana she will meet with President Ian Khama and with women leaders. She will also see a nature reserve.

Her trip comes as the United States starts gearing up for the 2012 presidential election, when her husband, President Barack Obama, hopes to hold on to the White House. Pictures of Mrs. Obama in Africa could appear in the campaign to appeal to black voters, a critical voting bloc for Obama's Democrats.

White House officials said her visit would advance her husband's foreign policy goals.

"This trip by the first lady is very directly connected to the president's agenda in Africa and the Obama administration's foreign policy in Africa," Ben Rhodes, President Obama's deputy national security adviser told reporters last week.

"It's no coincidence that she would be visiting countries that have embraced democracy, (and) in many respects, have shown that not only does their democracy deliver for its citizens, but it can provide a positive example for the neighborhood that these countries are in as well."

The first lady's previous official solo sojourn abroad was to Mexico.

She is joined on this trip by her two daughters, Sasha and Malia, as well as her mother.