(Reuters) - South African police opened fire on striking miners armed with machetes and sticks at Lonmin's Marikana platinum mine on Thursday, killing at least a dozen men in scenes that evoked comparisons with apartheid-era brutality. In the incident, filmed by Reuters television, officers opened up with automatic weapons on a group of men who emerged from behind a vehicle and started loping towards police lines. The volley of bullets threw up clouds of dust, which cleared to reveal bodies lying on the ground. President Jacob Zuma said he was "shocked and dismayed" at what appeared to be one of the bloodiest police operations since the end of white-minority rule in 1994 in Africa's biggest economy. "I have instructed law enforcement agencies to do everything possible to bring the situation under control and to bring the perpetrators of violence to book," he said in a statement. Police have refused to confirm the death toll from the operation to disperse 3,000 protesting drill operators who had massed on a rocky outcrop near the mine, 100 km (60 miles) northwest of Johannesburg. "The police, in order to protect their own lives and in self-defence, were forced to engage the group with force," they said in a statement. "This resulted in several individuals being fatally wounded, and others injured." The police ministry said that the officers acted as they did only after first trying to peacefully disperse the crowd. "The minister is of the view that given the volatility of the situation, police did their best," the minister's spokesman Zweli Mnisi said in a text message. "What should police do in such situations when clearly what they are faced with are armed and hardcore criminals who murder police?" A Reuters photo showed a dozen corpses lying on a patch of sandy ground, while a spokeswoman from the opposition Democratic Alliance said the overall toll could be as high as 38. The SAPA news agency said one of its reporters had counted 18 bodies. World platinum prices leapt as much as $30 an ounce - more than 2 percent - to a six-day high as the extent of the violence became apparent in the country with 80 percent of known reserves. Leaders of the radical Association of Mineworkers and Construction Union (AMCU), which was representing most of the strikers, accused police of a massacre. "There was no need whatsoever for these people to be killed like that," General Secretary Jeffrey Mphahlele told Reuters. Some commentators likened the scenes to apartheid-era footage of ranks of police opening fire on crowds of protesters in black townships. "I cannot think of a confrontation between protesters and police since 1994 that has taken place along these lines," said Nic Borain, an independent political analyst. "PREPARED TO DIE" Before the start of the operation by hundreds of police, officials said several days of talks with AMCU leaders had broken down, leaving no option but to use force to break the crowd, which had triggered the closure of the mine. "Today is unfortunately D-day," police spokesman Dennis Adriao said. Prior to Thursday, 10 people - including two policemen - had died in nearly a week of fighting between rival worker factions at the mine, the latest platinum plant to be hit by an eight-month union turf war. The Marikana strikers have not made their demands explicit, although much of the bad blood stems from AMCU's challenge to the two-decade dominance of the National Union of Mineworkers, a close ally of Zuma's ruling African National Congress. Before the police advance, AMCU president Joseph Mathunjwa, whose organisation has been on a big recruitment push in South Africa's platinum mines, said there would be bloodshed if police moved in. "We're going nowhere," he shouted through a loud-hailer, to cheers from the crowd. "If need be, we're prepared to die here." The unrest has forced Marikana's London-headquartered owner to halt production at all its South African operations, which account for 12 percent of global platinum output. Lonmin said it had lost the equivalent of 15,000 ounces of platinum from the six-day disruption, and was unlikely to meet its full-year production target of 750,000 ounces. Its shares fell to a four-year low, losing 6.7 percent in London and 7.3 percent in Johannesburg. In all, they have shed more than 13 percent since the unrest started at the weekend. At least three people were killed in a similar round of fighting in January that led to a six-week closure of the world's largest platinum mine, run nearby by Impala Platinum. That helped push the platinum price up 15 percent. Despite South Africa's dominance of the platinum sector, rising power and labour costs and a sharp drop in the price of the precious metal this year have left many mines struggling to keep their heads above water.