Tom Allard, Jakarta – Workers at the Freeport-McMoran gold and copper mine have been ordered to stay at home after another series of shootings on the road where an Australian, Drew Grant, was murdered over the weekend.

The latest attacks came as analysts pointed to a rivalry between the military and police as a likely source of the violence as the two elements battle for a share of the multi-million dollar stream of informal protection payments to secure the enormous concession.

An attack yesterday afternoon injured two police officers, and a Freeport vehicle was riddled with bullet holes on Tuesday afternoon, but there were no injuries in that attack.

Since Saturday at least five ambushes have occurred, killing three people and injuring several others. It is the worst violence at the controversial mine in seven years.

A spokesman for Freeport, Mindo Pangaribuan, said several hundreds workers who live in Timika have been told to stay away from the mine "until further notice".

While there has been a marked upgrade in security around Freeport's Grasberg mine in the Indonesian province of Papua, including the deployment of the police counterterrorism unit and mobile brigade, the attacks are being made with virtual impunity.

The sophistication of the ambushes, the apparent use of military issue weapons and the ability of the assailants to avoid detection has increased speculation that the perpetrators are either members of the security services, or have been trained by them.

Eben Kirksey, a University of California academic who has researched previously violence at Freeport, including the murder of two American teachers in 2002, points to a dispute between the military and police in Papua.

"The jury is out, but there's clearly a motivation for elements of the Indonesian military," he said. "Since a 2007 decree, the police is in charge of security at Freeport and they have been paid handsomely for it... $US8 million ($10 million) last year according to filings [to the US sharemarket] by Freeport," he said. "The TNI [Indonesian armed forces] wants a slice of that pie."

The Defence Minister, Juwono Sudarsono, said it was well known that there was a "lucrative" trade run by criminal syndicates in illegally mining the tailings from the mine. "You can earn between $US3000 and $US3500 per month," he said.

"My own speculation, and that's pure speculation, is that these are criminal groups from inside Papua and also outside of Papua who have seen this as a lucrative business... It maybe a battle over providing access to this type of business."