Just over a quarter of workers had returned on Monday to the platinum mine in South Africa where 44 men were killed last week in violent clashes, after mine owner Lonmin threatened to sack about 3,000 striking workers if they did not turn up.

A panel of investigators appointed by President Jacob Zuma is also expected at the sprawling Marikana mine about 100 kilometres (60 miles) northwest of Johannesburg, where 34 miners armed with spears, machetes and handguns were gunned down in a hail of police fire that brought back memories of apartheid-era violence.

Ten people were killed prior to the police shooting, including a shop steward from the National Union of Mineworkers (NUM), who was hacked to death.

"Attendance has started slowly but is now up to 27 percent. But it is unclear if the striking workers are returning," a Lonmin spokesperson told Reuters. About 3,000 striking workers at the world's No.3 platinum producer face an ultimatum to show up on Monday or be sacked.

Police spokesman Dennis Adriao said there had been no reported incidents on Monday morning.

"There is a high police presence and visibility," he said.

The strike was sparked by a spreading battle for membership between the NUM and the upstart Association of Mineworkers and Construction Union, which has accused the NUM of caring more about politics and personal enrichment than workers in mine shafts.

Hundreds of police have camped out at the mine, patrolling in small convoys of vehicles and conducting aerial surveillance by helicopter.

Zuma also declared a national week of mourning to remember those killed in the mine violence.

Union leaders have also said they were not sure if the striking workers would report to the shafts.

London-based Lonmin, which accounts for 12 percent of global platinum output, was forced last week to freeze mining as a result of the violence, but essential services such as ventilation have been maintained so the mines can quickly restart.

Company officials could not immediately say when ore would start coming out of the earth again.

The stoppage has driven the platinum price to six-week highs over $1,460 an ounce, but much of the industry remains unprofitable at a time when it is grappling with a wave of labour unrest.

Lonmin had already slashed spending plans before the latest flare-up of violence and may miss its annual production target of 750,000 ounces. - Reuters