JOHANNESBURG, South Africa – Police opened fire Thursday on striking workers at a South African platinum mine, leaving as many as 18 dead, according to authorities and news reports.

South African police officials confirmed that lives were lost in the shootings, captured on graphic Reuters news service video and tweeted, but they didn’t give casualty figures. There were conflicting news reports that 12 to 18 people had died.

The gunfire came when police moved in to try to disperse workers after a week of violence at the mine involving workers from competing unions armed with machetes, sticks and spears. The earlier clashes had left 10 people dead, including miners, security guards and two police officers reportedly hacked to death by workers.

In Thursday’s violence, the Reuters video showed dozens of police officers confronting a crowd of miners who were trying to rush at them. Police opened fire and continued shooting into a cloud of dust for about two minutes. When the dust cleared and the police advanced, a number of dead miners were seen lying on the ground.

South African President Jacob Zuma issued a statement Thursday saying he was “shocked and dismayed by this senseless violence.”

“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.

Other South Africans were horrified by the violence, with some comparing the shootings to the apartheid era when white security forces quelled township protests using live ammunition.

A police spokesman said officers did their best to handle a volatile situation, and accused heavily armed miners of opening fire first.

“Now what should police do in such situations when clearly what they are faced with are armed and hard-core criminals who murder police?” police spokesman Zweli Mnisi said. “We had a situation where people who were armed to the teeth, attacked and killed others, even police officers and, for the record, one of the firearms used was that of our deceased police officer.”

The trouble occurred at a mine at Marikana, about 40 miles northwest of Johannesburg, owned by Lonmin, the world’s third-largest platinum producer. Lonmin shut down operations when violent clashes broke out between striking workers six days ago as rival unions battled for dominance at the mine.