(Includes strong language in paragraph 10)
By Ed Cropley
JOHANNESBURG, Jan 29 (Reuters) - A new cellphone video of the police shooting of 34 miners in South Africa in August has piled more pressure on the security forces, showing officers bragging about the killings and undermining claims they fired in self defence.
Reuters television footage of some of the killings at Lonmin's Marikana platinum mine showed a dozen striking miners being cut down in a hail of police gunfire.
The images of the bloodiest security incident since apartheid shocked the world and severely dented the reputation of Nelson Mandela's "Rainbow Nation" and the ruling African National Congress (ANC), which faces an election next year.
However, the majority of miners died in and around a small cluster of rocks - known as a 'koppie' in Afrikaans - about 400 metres (yards) away and out of sight of reporters and television cameras.
It is here that multiple witness reports have spoken of police officers gunning down miners as they surrendered or shooting them in the back as they fled.
The cellphone footage from the koppie, aired on Britain's Channel 4 television late on Monday, shows a police officer lying on the ground behind a rock with his pistol drawn.
The images were shot by his colleague, also lying in the grass, with the barrel of his sidearm regularly moving into the frame.
The first officer indicates that a miner is on the move in front of them. A voice can then be heard shouting: "Wait, don't shoot him, don't shoot him."
Gunfire is then heard, and the video cuts to the body of a man in jeans lying in the grass.
Moments later, another officer off-camera can be heard boasting about killing the man. "That motherfucker. I shot him at least 10 times," the officer says.
Channel 4 said the body had been identified and the man had been shot 12 times.
Police spokesman Dennis Adriao declined to comment on the latest footage.
The police have said they resorted to lethal force after coming under fire from some armed miners, although post mortem reports released to a judicial inquiry indicated 14 of the Marikana victims had been shot in the back.
The inquiry, chaired by a retired judge, is due to wind up in the middle of the year. Its findings are likely to be damning of the security forces and could have implications for President Jacob Zuma as he heads for an election due in just over a year.
Lonmin expressed horror at the bloodshed and, five weeks later, agreed a hefty pay hike that saw the striking miners return to work.
(Reporting by Ed Cropley; Editing by Jon Herskovitz, John Stonestreet)