Environmental organisation WWF called on the government Wednesday to investigate the death of a critically endangered Sumatran elephant allegedly poisoned at an Indonesian oil palm plantation.

A ranger at the plantation in Aceh Jaya on Sumatra island said he found the 18-year-old female elephant dying on Monday and that locals reported they had seen it walking around with a calf earlier that day.

"We call on the authorities to investigate how the elephant died. If she died from poisoning, we hope authorities will do something about educating locals," WWF's Aceh programme leader Dede Suhendra told AFP.

"People here in Sumatra who own plantations and farms often kill elephants, tigers too, because they see them as pests."

Mukhtar, the ranger, said he believed the elephant had been poisoned.

"When I found her, she was foaming at the mouth and bleeding from the rectum, which are strong signs of poisoning," he said, adding that he was unable to save her with medicine.

Mukhtar said the elephant's calf was "crying" and "making noises" of distress as it stood by its mother dying on the ground.

Suhendra said that conflict between animals in the jungle and humans had increased in the past decade as swathes of forest are cleared for agriculture.

WWF changed the Sumatran elephant's status from "endangered" to "critically endangered" in January, largely due to severe habitat loss driven by oil palm and paper plantations.

There are less than 3,000 Sumatran elephants remaining in the wild, according to the International Union for Conservation of Nature, marking a 50 percent drop in numbers since 1985.