President Cyril Ramaphosa's office had earlier issued a statement of well-wishes for Mlangeni, who celebrated his birthday last month, saying he had been admitted to 1 Military Hospital in Thaba Tshwane in the capital Pretoria on July 14 with an abdominal complaint.

"President Ramaphosa has learnt with deep sadness of the passing away overnight of the last remaining Rivonia Trialist... Andrew Mekete Mlangeni," the Presidency later said in a Twitter post.

Mlangeni was the only man still alive from the group of political activitsts who were in the dock in the so-called Rivonia Trial, after the death in April of 87-year-old Denis Goldberg, who was the only white member of the group.

Mlangeni was born in 1925 in Johannesburg's sprawling township of Soweto, and left school at 12 to look for work and help his mother take care of the family, his father having passed away.

In the 1940s he worked in several industries and factories where he experienced labour exploitation, culminating in his participation as a bus driver in a strike for better working conditions and wages.

Mlangeni joined the youth league of the now-governing African National Congress (ANC) in 1951 and the party itself in 1954 and was among the first people to be sent for military training outside South Africa in 1961.

On his return in 1963 he was arrested after state witnesses said he was one of the people responsible for recruiting and training an armed force. He was found guilty and sentenced to life imprisonment on Robben Island, where he spent more than 20 years.

At Mlangeni's birthday celebration last month, Ramaphosa said the struggle veteran had in his later years been the "conscience" of the ANC, which has governed South Africa since the first democratic elections in 1994 which saw Mandela become the country's first black president.

Ramaphosa said over the years Mlangeni had encouraged and supported the ruling party when it did well and steered it back on course when it faltered.

"He (Mlangeni) has not hesitated to speak out when necessary," Ramaphosa told those gathered at the birthday party.

"It has been of great concern to him, and is a concern we share, that 26 years into democracy we have still not fully met the developmental aspirations of our people, and that this is an affront to human dignity."

African News Agency