WARNING: Viewers may find this footage distressing Reuters

South Africa has suspended eight police officers after the death of a man they tied to the back of a police van and dragged along the road while bystanders looked on.

Video footage showing the treatment of Mido Macia, in Daveyton, east of Johannesburg, has once more focused attention on South Africa's police force, already dogged by allegations of brutality, corruption and incompetence.

In the amateur video footage (warning: contains images that some may find distressing), published by South African newspaper, the Daily Sun, Macia's hands are tied to the rear of a police van behind his head before it moves off. Just over two hours later he was found dead in a local police cell, according to the Independent Police Investigative Directorate (IPID). A postmortem gave the cause of death as head injuries with internal bleeding.

The video provoked outrage with President Jacob Zuma labelling it "horrific, disturbing and unacceptable. No human being should be treated in that manner." He has instructed the minister of police to investigate the matter.

Police chief Riah Phiyega said the eight officers involved had been suspended and the station commander would be removed from his duties. "We would like to assure the country and the world that what is in the video is not how the South African police service in a democratic South Africa goes about its work," she said.

The IPID responded by launching an inquiry and giving details of the police version of events. The police account alleged that Macia, 27, a taxi driver from Mozambique, assaulted an officer and took his firearm after officers asked him to move his taxi because it was obstructing traffic. They admitted only that there was a "struggle" to get the taxi driver into the police van.

But a further video (warning: contains images that some may find distressing) published by the Daily Sun and provided to the Guardian casts doubt on the account. The new footage suggests Macia did not grab the gun or use violence against police, only struggling to free himself as police seized him and lifted him off his feet.

Amnesty International's human rights organisation's southern Africa director, Noel Kututwa, said the incident was "the latest in an increasingly disturbing pattern of brutal police conduct in South Africa". It comes after a series of setbacks for the South African police force, struggling to demonstrate that its low paid, reputedly poorly-trained, officers can be trusted to uphold – or even obey – the law. Last week, the case against Oscar Pistorius, accused of murdering his girlfriend Reeva Steenkamp, was undermined when the lead investigating detective was removed from the case after being charged with seven counts of attempted murder himself. Last year's Marikana shootings, in which police opened fire on a crowd of striking miners, killing 34 at a platinum mine northwest of Johannesburg, are being investigated by a judicial commission.

Macia's case also evoked memories of the death of Andries Tatane, a mathematics teacher and community activist in 2011, which was also captured on video. Tatane was attacked at a peaceful protest march by 12 policemen who beat him with batons, kicked him and shot rubber bullets into his chest at close range.

The dispute between Macia and police officers began just before 7pm on Monday. Video shows him gesticulating at an officer but, although there are small gaps in the footage, there is no indication that Macia laid a hand on him. Daily Sun publisher Jeremy Gordin denounced the police account as "a tissue of lies".

Other officers move in and Macia is dragged away, being lifted head-over-heels as police attempt to get him into the police van. He is eventually tied to the van. Onlookers shout that they are going to film the incident and a bystander can be heard shouting in Zulu: "What has this guy done?"

The van moves off while Macia tries in vain to keep step. It then stops, two police officers pick up his legs and drop them to the ground as the vehicle picks up speed and drives off, beyond the view of the camera. The IPID said Macia was found dead in a police cell at 9.15pm.

South African police said the national commissioner, Riah Phiyega "strongly condemned" what had happened and urged people "to remain vigilant and continue to report all acts of crime irrespective of who is involved".

As well as provoking further soul-searching about state violence, Macia's death may also raise fresh concerns about the country's treatment of immigrants. In 2008, Mozambicans were among migrants targeted by rioters, and attacks against foreigners have continued, including allegations of police brutality.

Amnesty's 2012 annual report documented allegations against the South African police of excessive force, torture, rape and "extrajudicial executions". It said the IPID received 720 new cases for investigation of suspicious deaths in custody or in other policing contexts from April 2011 to March 2012.

The Institute for Security Studies in Pretoria has reported that the number of people shot dead by police doubled in the four years to 2010. Deaths in police custody or resulting from police action numbered 860 in 2009-10, against an average of 695 deaths a year from 2003-2008.

Have you been affected by a similar incident in South Africa? Please email us on guy.grandjean@guardian.co.uk