Cape Town, South Africa ? Wearing a T-shirt with the words “HIV-positive” emblazoned across the front, former Nelson Mandela declared war on AIDS Thursday, and urged people to practice safe sex or abstain completely.

The 84-year-old former president, who led the fight against apartheid and remains South Africa’s most revered public figure, recently has emerged as a champion of the fight against AIDS.

One in five adults in the country is estimated to be HIV-positive, and a study by the Medical Research Council warned that up to 7 million South Africans could die of the disease by 2010 unless radical action is taken.

“This is a serious matter, it’s a war,” Mandela said on a visit to a clinic in the sprawling Khayelitsha township on the outskirts of Cape Town, where Medecins San Frontieres monitors 3,000 AIDS patients.

Aides say Mandela now devotes 60 percent of his time to fighting the disease. In recent months, a foundation Mandela started has launched an initiative to secure treatment for 9,000 AIDS sufferers who would otherwise be unable to afford it.

Mandela announced plans last week for a concert featuring some of the world’s top entertainers — including U2, Macy Gray and Shaggy — to raise money for AIDS victims. The concert will be in February on Robben Island, where Mandela was imprisoned for nearly two decades by the apartheid regime.

Mandela was freed in 1990 and was elected president in 1994 in South Africa’s first all-race election. The Nobel Peace Prize winner stepped down as president in 1999.

As president, Mandela mainly left the AIDS crisis to subordinates. When the government launched a major anti-AIDS drive, Mandela had then-Deputy President Thabo Mbeki deliver its message over state television. Many believe the step was taken because it was viewed as improper in African culture for an elderly gentleman to talk openly about sex.

Former South African President Nelson Mandela, right, and AIDS activist Zackie Achmat visit the Nolungile Clinic and Community Health Center in Khayelitsha, Cape Town, South Africa. Mandela has emerged as a champion of the fight against the country's rampant AIDS epidemic.

But on Thursday, Mandela, gray-haired and walking with a cane, spoke freely about using condoms, the necessity for people to remain faithful to their partners and for AIDS sufferers to be accepted by their communities.

He urged young people to wait as long as possible to have sex.

“HIV is like any other disease,” he sternly told a crowd of several hundred people. “We must love people who have HIV. To stigmatize people — you are not acting like human beings.”