"It is with an indescribable sense of loss that the Chairperson of the African Union Commission, Moussa Faki Mahamat learnt of the passing of Kenneth Kaunda, the first president of Zambia and one of the Founding Fathers of the Organization of African Unity (OAU)," said an AU statement.
During the commemoration of this year's African Day, the AU honored Kaunda, who was 97 years old, with a special award for the role he played in and the immense contribution he made to the liberation of Africa and its people.
"Africa has lost one of its finest sons," the chairperson said.
Muhamat said Kaunda's championing of the Frontline States to defeat Apartheid and white minority rule in Southern Africa laid the foundation for regional integration today.
Zambian President Edgar Lungu has announced a 21-day mourning period for the former president.
"On behalf of the entire nation and on my own behalf I pray that the entire Kaunda family is comforted as we mourn our First President and true African icon," Lungu wrote on his Facebook page on Thursday.
Born in 1924, Kaunda led Zambia's independence struggle and served as the first president of the country from 1964 to 1991.