Eight South African police officers have been arrested over the death of a Mozambican man who was apparently dragged behind a police vehicle.
An investigation was launched after video footage emerged showing the man hauled through the streets with his hands cuffed to a police van.
Police Commissioner Riah Phiyega thanked people for revealing "callous and unacceptable behaviour".
President Jacob Zuma called the incident "horrific" and "unacceptable".
The eight officers were initially suspended pending an investigation. It was later announced that they had been arrested and would appear in court on 4 March.
Taxi driver Mido Macia, 27, died of head injuries and internal bleeding after his arrest in Daveyton, east of Johannesburg, an initial post-mortem found.
He was reportedly detained for parking his vehicle in a way that blocked traffic.
The video, apparently recorded by a bystander on a mobile phone on Tuesday, shows a large crowd watching as uniformed policemen tie him to a van, dragging him as they drive away.
Public anger grew after the footage was broadcast on television.
South Africa's police watchdog - the Independent Police Investigative Directorate - is examining the video as part of its investigation.
'Shock and outrage'
The BBC's Milton Nkosi in Johannesburg says a small group of protesters, mostly women, gathered on Friday morning outside the police station where the 27-year-old taxi driver died in the holding cells.
Some of the chants accused the police of brutality.
The South African Police Service expressed "extreme shock and outrage" at the mobile phone footage.
"From the video which has gone viral, it is obvious that the rights of Mido Macia were violated in the most extreme form," it said in a statement,
"The behaviour displayed in that video, when it is committed by police who are expected to serve and protect, is to be abhorred," it added.
South Africa's police force was already under intense scrutiny after officers shot dead 34 striking miners last August.
Its credibility was also dented when it emerged that the lead detective in the murder case against athlete Oscar Pistorius was himself accused of attempted murder.
The police service said it would give its full support to the Independent Police Investigative Directorate as it looked into Mr Macia's death.
"We fully support the principle of police being policed and we shall be transparent about the outcome of the investigation," it said.
Justin Ndlovu, the chair of the Benoni Taxi Association, said he knew Mr Macia and had last seen him last week.
"He was a very humble guy; he leaves behind one child in South Africa," he told the BBC.
"His brother died last year and he had become the guardian of his brother's wife and three children [also living in South Africa]."