Officials say ongoing violence at a platinum mine in South Africa has killed at least nine people.

The violence is happening at a Lonmin PLC mine near Marikana, a town about 70 kilometers (40 miles) northwest of Johannesburg. In a statement Monday, Lonmin said at least four of the mine’s workers have been killed in ongoing attacks. That includes two security guards who died Sunday when their car was set ablaze by angry miners.

Police Brig. Lindela Mashigo said two officers and three others were killed in more violent protests Monday.

Lonmin said the violence started when workers walked off the job Friday over pay, and it has escalated between two rival mining unions.

Lonmin is the world’s third largest platinum producer. South Africa is one of the world’s coal, platinum and gold-producing giants.