South African President Jacob Zuma announced Friday a probe into the deaths of 34 miners in a police crackdown on a wildcat strike, in the deadliest protest since apartheid.

Police at the Marikana platinum mine run by Lonmin, the world's number three producer, insisted they acted in self-defence against hundreds of workers who stormed through teargas and rubber bullets trying to attack officers with gunfire, machetes and clubs.

But the nation recoiled from what local media quickly dubbed the "Marikana massacre", drawing comparisons to the deadliest apartheid atrocities, chiefly the 1960 Sharpeville massacre when white police killed 69 black protesters.

As the death toll mounted during the day, Zuma cut short a visit to a regional summit and flew to the mine, vowing to uncover the cause of the killings.

"It is clear there is something serious behind these happenings and that's why I have taken a decision to establish the commission (of inquiry) because we must get to the truth," Zuma said.

"This is a shocking thing. We do not know where it comes from and we have to address it.

"This is unacceptable in our country, which is a country that everyone feels comfortable in. A country with a democracy that everyone envies."

The White House said Friday that the United States was "saddened" by the deaths and expressed confidence in a government probe.

"The American people are saddened at the tragic loss of life," White House deputy press secretary Josh Earnest told reporters.

"We are confident that the South African government will investigate the facts around this case and, as always, we encourage all parties to work together to resolve the situation peacefully."

Police chief defends force

Police chief Riah Phiyega stood by her force, saying officers only used live ammunition after negotiation and crowd control tactics had failed.

"The militant group stormed toward the police, firing shots and wielding dangerous weapons," she said.

"Police retreated systematically and were forced to utilise maximum force to defend themselves."

So far 259 people have been arrested over the clash that left 34 dead and 78 injured, she said. Ten people, including two policemen, had died in earlier unrest at the mine.

Some workers at the mine were on a week-long wildcat strike demanding a tripling of their wages from the current 4,000 rand ($486, 400 euros) a month.

With little official information about the victims 24 hours after the incident, residents of a shantytown near the mine were fuming.

"Now I want to see my husband because his baby is crying," said Asakhe Mayaphi, 25, gesturing to the shacks behind her.

She last saw her husband Mzubanzi early Thursday, and did not know if he had been hurt or killed.

London-listed Lonmin said it would help the families identify and bury the dead. Many of the wounded were taken to a nearby hospital run by the mine.

It was the deadliest police action in South Africa since 1985, when more than 20 blacks were shot dead by apartheid police in Cape Town as they marked the 25th anniversary of Sharpeville.

This time the gunfire came from a mostly black police force, shooting at poor black miners who say their living conditions have hardly improved in the 18 years since apartheid yielded to all-race democracy.

"I always thought that the Sharpeville massacre was history and it would never happen again. What we experienced yesterday under the democratic government was similar to Sharpeville," said Joseph Mathunjwa, head of the Association of Mineworkers and Construction Union (AMCU).

Before Thursday 10 people had already died at Marikana in attacks blamed on rivalry between the radical new AMCU and the powerful National Union of Mineworkers, a major ally of the ruling African National Congress.

The two unions condemned that violence, denied taking part in the killings and blamed each other for the troubles.

Zuma's handling of the unrest could prove pivotal as he tries to stamp out leadership challenges within the ANC, ahead of the elective conference in December where he will seek a second term as party boss.

The NUM is one of South Africa's most powerful unions, having produced several top ANC leaders, including Deputy President Kgalema Motlanthe -- seen as a potential challenger to Zuma.