A deadly shooting rocked the already troubled copper and gold mining firm PT Freeport Indonesia in Papua on Friday, leaving three men dead and three others badly injured, according to initial reports.

Witnesses said unidentified gunmen attacked a Freeport security truck at around 3:45 p.m. local time while it was passing mile 36 on Tanggul Timur road near Nayaro village, nearly the same spot of another Freeport-related shooting in April.

The truck carried two military officers — Second Sgt. Eko and First Pvt. Pratu Tobias — and two employees working for the company’s security management unit — Roy Maleke and Beny Thomas.

Unconfirmed reports say a man was found dead inside the truck, which caught fire after the shooting. Two men were found dead outside the vehicle.

Papua Police spokesperson Sr. Comr Wachyono confirmed that three men died from the shooting and that a second security team that approached the vehicle to rescue the victims was also attacked by the mysterious gunmen, injuring one security officer and another military officer.

He added as of Friday night, joint security forces from the Mimika District Police, Papua Mobile Brigade Unit and Freeport’s security force were still securing the crime scene.

The shooting near Freeport’s site came on the heels of the death of Petrus Ayamseba, who was shot dead this week by the police during a rally by Freeport workers demanding a salary increase. Petrus, 36, worked for PT Pangansari, a firm that provides food for Freeport workers.

Human rights organizations condemned the violence. An investigation into the incident is ongoing.

Freeport employees have been under constant threat of violence since July 2009.

In April, Daniel Mansawan and Harry Siregar, both Freeport security officials, were found dead in their burned-out car at the mile 37 marker on Tanggul Timur road. Although the cause of their deaths was confirmed to have been the fire, the police said they found bullet holes.

Just a day before Daniel and Harry were killed, two other Freeport employees — Abdul Simanjuntak and Agus Patah — were fired upon while driving. They were injured by shards of glass from the windshield.