The African Union has paid its respect to Winnie Madikizela-Mandela.
In a statement on its website, African Union Commission chairperson Moussa Faki Mahamat said he has learned, with "great shock and profound sadness of the death of Madikizela-Mandela".
The AU chief described her as a "fearless campaigner who sacrificed much of her life for freedom in South Africa".
The struggle icon died on Monday at the Netcare Milpark Hospital in Johannesburg.
"She never relented in her struggle or wavered in her commitment, despite imprisonment, banishment, and decades-long seperation from her then husband Nelson Mandela during his imprisonment," Mahamat said.
"Winnie Madikazela-Mandela paved the way for women in the struggle to end apartheid, and fought relentlessly for their rights and welfare in her country."
Madikizela-Mandela was awarded a lifetime achievement award in 2017 from the African Union Commission.
Kenyan President Uhuru Kenyatta has also paid tribute to Madikizela-Mandela.
Kenyatta said that Africans should emulate the struggle icon.
Several other African heads of state, including Ugandan President Yoweri Museveni, have also paid tributes.
This evening, I learned that Winnie Madikizela-Mandela had left us. The news is saddening, for we have lost a heroine and a liberator.— Uhuru Kenyatta (@UKenyatta) April 2, 2018
May her courage inspire us to make the most of the liberty she won for us; may her family be comforted by the memory of her heroic life; and may she rest in perpetual peace.— Uhuru Kenyatta (@UKenyatta) April 2, 2018
Very sorry to hear about the death of comrade Winnie Mandela. I salute her contribution to the resistance in South Africa, especially during the time Mzee Mandela was in prison.— Yoweri K Museveni (@KagutaMuseveni) April 2, 2018