Four rare Sumatran elephants were found dead in northwestern Indonesia near an oil palm plantation and are believed to have been poisoned by villagers, a conservationist said Thursday.

The carcasses of the protected giant animals were in a forest 560 miles (900 kilometers) from the capital, Jakarta, said Eddy Santoso, head of the local Conservation and Natural Resources Agency. The forest land has been rented by the government to local farmers for commercial purposes.

The latest elephant carcass was discovered partly burnt Thursday, making it difficult to determine whether it was male or female, Santoso said.

He said it was apparently burned with used tires.

On Monday the decaying carcass of a six-year-old female elephant was discovered near two other dead females found last Thursday.

Just 3,000 Sumatran elephants remain, some of them in the forest in Riau province. Parts of the forest were converted into oil palm plantations managed by villagers with the assistance of the state-owned plantation company Perkebunan Nusantara.

Santoso said he suspects the elephants were poisoned by villagers running a plantation for oil palms, which are used to make palm oil, in an adjoining forest.

Elephants, confronted by dwindling jungle, sometimes run amok in farmland or villages, trampling crops and killing humans.

"Maybe the villagers were worried the wild elephants would attack their plantations," Santoso said. "They probably scattered poison there."

Last month, conservationists came upon two giant males that had been poisoned with cyanide-laced pineapples in the same area, with their tusks removed.

Police and the agency were investigating the latest case.

Indonesia's endangered elephants, tigers, rhinos and orangutans are increasingly threatened by shrinking jungle habitat, which is cut and burned to make way for plantations or sold as lumber.

Palm fruit is pressed to make palm oil, used in cosmetics, food and increasingly for clean-burning fuel. The profitable commodity is one of Indonesia's leading export products and a billion-dollar industry.