Authorities said they had yet to determine whether members of the separatist Free Papua Movement (OPM) were behind the killing of an Australian Freeport technician early on Saturday and a local contract security officer the following morning.

Freeport’s copper and gold mine has been a source of tension in the area since it opened more than 40 years ago. In recent decades it has been a focal point for the region’s low-intensity OPM rebellion.

Freeport Indonesia is the largest single taxpayer to the Indonesian government.

Saturday’s shooting of Drew Grant was the first attack on a foreigner associated with Freeport since the 2002 ambush of a Freeport school bus in which two Americans were killed. After the police initially accused the military of involvement in that incident, the US Federal Bureau of Investigation helped the authorities capture and secure the conviction of a separatist commander.

On Sunday senior police officers were careful not to blame anyone for the latest shootings, which they said were carried out using military and police-issue rifles.

Australia’s foreign minister, Stephen Smith, said two Australian federal police officers had flown to Papua at Jakarta’s request to help with the investigation into Mr Grant’s murder.

Both shootings occurred just over 50 miles north of the town of Timika on the road to Freeport Indonesia’s mining operations. Five people were injured in the incident on Sunday.

Brigadier General Sulistyo Ishak, a police spokesman, said that while Saturday’s attack appeared to be that of a lone gunman, the shooting of the security guard, Markus Rattealo, could have involved more attackers. The vehicle he was travelling in was “sprayed” with bullets and five other people were injured.

“After the incident, Detachment 88 [anti-terror personnel] had a gun battle with the unknown gunmen,” Gen Ishak was quoted as saying by Antara, the state news agency.

Mindo Pangaribuan, a Freeport spokesman, said the violence was unexpected. “There was no indication that anything like this might occur,” he said, adding that mining operations were “continuing normally”.

Indonesia’s presidential election last Wednesday, which authorities feared might have been an occasion for violence, passed relatively peacefully in Papua.

Most Papuans believe Jakarta has treated them unfairly since annexing the western half of New Guinea island in 1969 after a dubious vote. The locals believe the government milks their rich resources while undertaking little development in return.

Jakarta granted Papua special autonomy in 2001 but progress has been patchy. Pro-independence militants have waged a long-running insurgency against Indonesian rule in Papua, which is off-limits to foreign journalists without special permission.