JAKARTA, Indonesia - Three more people were wounded by gunfire Wednesday at the world's largest gold mine, the latest ambush targeting employees of U.S. conglomerate Freeport in Indonesia's underdeveloped Papua province.

It is the sixth attack by unidentified gunman on the Phoenix, Ariz.-based company in under two weeks, and marks the worst violence at Freeport since the 2002 killing of three schoolteachers, including two Americans.

The unrest -- which has killed two people and wounded dozens since the shootings began July 11 -- also comes as Indonesia recovers from twin suicide bombings in the capital, Jakarta, last Friday, that killed seven people and wounded dozens, including two Freeport executives.

Freeport said in a statement that several employees and their security detail were fired upon Wednesday while driving along the road where the previous shootings occurred to help a broken down vehicle. A mechanic and two policemen were shot, it said.

National police spokesman Nanan Sukarna said the attack was carried out by unidentified gunmen and that the three injuries were caused by shrapnel. The culprits escaped.

Two other policemen died Wednesday when their car flipped "while driving at high speed through a dangerous area" a few miles (kilometres) away, said local police chief Lt. Col. Godhelp Mansnembra.

Freeport, citing the police, said the incidents did not appear to be related.

Wednesday's attack comes a day after authorities said they rounded up 15 suspects allegedly behind the recent killings. Freeport CEO Richard Adkerson said Tuesday that six of them had been charged, including a man who apparently acknowledged being a sniper.

"We have been assured from the highest levels of government in Indonesia they are committed to provide safety for our people and for our operations," Adkerson said in a conference call detailing the company's latest earnings.

The violence is an unwelcome surprise for President Susilo Bambang Yudhoyono, who is firmly on track to win a landslide victory that will put him in office until 2014, partly thanks to his good reputation in combating Islamist militancy.

The Antara state news agency initially reported that Wednesday's shooting targeted a convoy of 12 buses returning hundreds of employees who have been unable to return to work. The road targeted by the shootings links the Grasberg mining complex and the town of Timika, and has been declared off limits unless employees travel with security.

A PT Freeport spokesman in Indonesia, Mindo Pangaribuan, said early Wednesday that "secure transportations have been arranged to transport personnel and deliver supplies." The buses were turned back because of the gunfire, but Freeport said in its statement that no shots were fired at the bus convoy.

Papua is home to a four-decade-old, low-level insurgency against the government, and members of the Free Papua Movement -- who see Freeport as a symbol of outside rule -- were initially blamed by authorities for the latest violence.

However, some experts believe the shootings resulted from a rivalry between the police and military over multimillion-dollar illegal gold mining or protection businesses at the mine. Others blame criminal gangs.

It is difficult to get accurate information out of Papua, a remote and highly militarized area that is off limits to foreign journalists.

Freeport has been targeted with arson, roadside bombs and blockades since production began in the 1970s during the U.S.-backed Suharto dictatorship. It is also regularly the focus of protests by local residents who feel they are not benefiting from the depletion of Papua's natural resources.

The recent shootings that began earlier this month have killed an Australian mining expert and a contract security guard. More than a dozen others have also been hit by bullets.

Papua, a desperately poor mountain province, lies on the western half of New Guinea island, some 2,100 miles (3,400 kilometres) east of the capital, Jakarta. Formerly known as West Papua, the territory with a population of around 2.5 million was transferred from Dutch to Indonesian rule in the 1960s after a U.N. sponsored vote by community leaders that has been widely dismissed by academics as a sham.