Gunmen shot dead three people Friday at a strike-ridden gold and copper mine in Papua, its US operator said, raising the number of deaths this month at the troubled facility to eight.

The Grasberg mine in the eastern Papua region, operated by US company Freeport McMoRan and one of the largest in the world, has been trouble-plagued since miners declared a month-long strike over wages on Sept. 15.

Grievances erupted into deadly violence this month when workers clashed with police, and unknown gunmen targeted contract workers brought in to replace strikers.

"Unidentified gunmen opened fire and three people were killed and one was wounded," in the latest incident Friday, Ramdani Sirait, a spokesman for Freeport's Indonesian subsidiary, told AFP.

He added that one of the victims was a Freeport contract worker, and that the identities of the three others was not immediately known. All were shot inside the mining area, he said.

Sirait said the incident occurred near a shooting last Saturday when three contract workers were shot dead in similar circumstances. "Police are now investigating the case," Sirait said.

In addition, two mine workers were killed in an Oct. 10 clash between police and striking miners. More than 8,000 of Freeport's 23,000 workers have been on strike, vowing to stay away from work until Nov. 15.