The letter was sent to Zuma on Friday by the miners' lawyers, Maluleke, Msimang and Associates, demanding that the president use his powers to secure their release.

In the letter, the lawyers questioned how the miners could be charged with the murders.

"It is our instruction to inform you that it would be the understatement of the century to call this turn of events bizarre in the extreme.

"It is inconceivable the South African state, of which you are the head... can genuinely and honestly believe or even suspect that our clients murdered their own colleagues and in some cases, their own relatives," the letter read.

On August 16, police opened fire on striking workers gathered on a hill near Lonmin's Marikana mine, in North West, killing 34 of them and wounding 78.

When the 270 men were arrested, they were initially charged with public violence but the National Prosecuting Authority (NPA) changed the charges to murder and attempted murder on Thursday.

Maluleke, Msimang and Associates asked Zuma to secure the prisoners' release by 1pm on Sunday, failing which the legal firm would launch an urgent high court application compelling him to do so.

Such an application would draw on the fact that Zuma's appointed judicial commission of inquiry into the deaths had not yet submitted its report.

"If the South African state is correctly awaiting the outcome of the inquiry in order to determine the possibility of criminal charges, how can the same state logically sustain its actions in charging our clients before the Enquiry has even started its work?"

Unions, the mine owners and the police had been exempted from prosecution until the report was complete, and so it was unclear why this protection was not afforded to the miners, the letter continued.

"At the risk of stating the obvious, the fact that it was the police who killed the 34 deceased protesters [sic].

"It was admitted by the national police commissioner [Riah Phiyega]... Her only qualification was to the effect that the police had killed the protesters in self defence. That they killed the protesters is not in dispute."

Presidency spokesman Mac Maharaj said he had not received confirmation that the letter had been received by the president's office in Pretoria.

He said Zuma could only intervene in the matter through Justice Minister Jeff Radebe.

On Friday, justice department spokesman Mthunzi Mhaga described the lawyer's demand for the men's release as "extra-ordinary".

"If they are adopting that stance, it would be an extraordinary route to explore from a legal point of view," he said.

"We would expect them to approach the courts."