(REUTERS) -- Impala Platinum , the world's second-largest platinum producer, said on Tuesday the costs of an illegal strike at its key Rustenburg operation in South Africa have reached 100,000 ounces and a loss of income of 2 billion rand ($263.66 million).

The strike, in its sixth week, has been marked by violence and a turf battle between unions. Implats said four more workers had been attacked in a sign that tensions remain.

Although there were no violent incidents over the weekend, there were assaults on four people last night and early this morning, with one severely injured, the company said in a statement.

It also described the strike as an attempt to destabilise the company.

Three workers have been killed during the violent strike at the world's largest platinum mine.

The dominant National Union of Mineworkers has faced a challenge from the upstart Association of Mineworkers and Construction Union but no one has been explicitly blamed for the violence.

Many of the attacks have been on those who want to return to work.

Spot platinum prices have gained about 16 percent since the troubles at Rustenburg began on Jan. 12.

Implats fired over 17,000 workers for taking part in the illegal stoppage but has offered to rehire up to 15,000. Workers have until 1300 GMT on Wednesday to reapply.