* Officer boasts of shooting miner "at least 10 times"
* Inquiry chairman said footage first seen in November
* ANC under pressure from sector in turmoil
By Ed Cropley
JOHANNESBURG, Jan 29 (Reuters) - A cell phone video broadcast this week of the police shooting of 34 miners in South Africa last year has piled more pressure on the security forces, showing officers bragging about the killings and undermining claims that 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 bullets.
The images of the bloodiest security incident since apartheid shocked the world, and dented the reputation of Nelson Mandela's "Rainbow Nation" and the ruling African National Congress (ANC), which faces an election next year.
Since then the pay strikes have abated, but turmoil in the sector has continued, with the world's biggest platinum producer, Anglo American Platinum Ltd, infuriating miners and the ANC alike with plans to mothball mines accounting for 3 pct of South Africa's workforce.
Most of the Marikana victims died in and around a small cluster of rocks - a 'koppie' in Afrikaans - about 400 metres (yards) away from the main confrontation, 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 cell phone footage from the koppie, aired on Britain's Channel 4 television, shows a police officer lying on the ground behind a rock with his pistol drawn.
The images were shot by a 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 can be heard off-camera 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, which was submitted by police to an inquiry into the killings in the city of Rustenburg, 120 km (70 miles) northwest of Johannesburg, according to inquiry officials.
Ian Farlam, the retired judge heading the probe, said the footage had been viewed by the inquiry in November and cautioned against reading too much into it.
"The commission is of the view that it is premature to draw conclusions from the video footage that is included in the broadcast," he told the inquiry, according to local media.
The police have said they resorted to lethal force after coming under fire from some armed miners. Post mortem reports indicated 14 of the Marikana victims had been shot in the back.
The Farlam inquiry 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.
Anglo American Platinum, which has announced plans to lay off 14,000 workers and close two mines, said on Tuesday that talks with the government and unions to mitigate the fallout had been "constructive".