Other prosecutors said separate charges would be filed against the Newmont unit involved in the case, PT Newmont Minahasa Raya. The six executives include two Americans, an Australian and three Indonesians.

"As soon as we receive the dossier, we will prepare the indictment, and hopefully by mid-December it will be handed over to the court," Worotikan said. In Indonesia, the lodging of an indictment with a court amounts to the filing of formal charges.

A government-commissioned probe found sediment in Buyat Bay in North Sulawesi, near a gold mine run by Newmont Minahasa Raya, had significant levels of arsenic and mercury.

Newmont denies that the bay, 1,400 miles (2,200 km) northeast of Jakarta, was contaminated by its mining and says it has followed Indonesian laws.

In Denver, Newmont spokesman Doug Hock said the company had no official comment other than to reiterate it was confident the facts would show the company did not pollute the bay and that people were not sickened by its operations.

Rubi Purnomo, a Newmont spokesman in Jakarta, said, "We will continue to cooperate with the investigation."

Newmont shares fell nearly 3 percent in morning trade on the New York Stock Exchange, but that was attributed to UBS downgrading the stock because it has risen 22 percent in the past four months.

Indonesian police had already named the executives as suspects while prosecutors decided whether to formally charge them. Five were detained for weeks over the matter.

Worotikan said they could be picked up again.

"We will see whether it is necessary or not to detain them. However, they have been cooperative," he said.

Charges of breaching environmental rules carry jail terms of up to 15 years in Indonesia if people are proven to have died or become seriously ill as a result of pollution, police say.

Legal articles cited by the prosecutors on Tuesday relate to rules that carry jail terms of up to 10 years for pollution.

DELICATE CASE

Industry organisations have agreed with the US embassy that the handling of the case, especially the detention of the executives, could be a hurdle to foreign investment.

Environmentalists say Indonesia has been lenient about polluters in the past and the case should be vigorously pursued.

The government-commissioned findings were the latest of several studies on Buyat Bay after some villagers filed a $543 million lawsuit against Newmont, charging waste from the mine had caused serious illnesses and ruined the local fishing industry.

Newmont has said it was vindicated by two earlier studies -- one by the Indonesian government and another by the World Health Organisation -- which concluded Buyat Bay was not polluted.

Either way, the case has alarmed foreign miners over the growing difficulty of doing business in Indonesia's outlying regions. Investment in the sector has slumped over vague regulations, illegal mining and tough environmental rules.

The Minahasa mine was closed in August due to depleted reserves and the company had been carrying out reclamation work. The accusations relate to when the mine was operational.

Indonesia is a major source of copper, gold, coal and tin.