Indonesian authorities suspect a Sumatran elephant found dead in a palm oil plantation may have been poisoned or electrocuted, marking the second time in a week a carcass of the critically endangered animal has been discovered, officials said.

Only about 2,400-2,800 Sumatran elephants are left in the world, putting them on the brink of extinction, according to the World Wildlife Fund (WWF).

The 25-year-old female elephant, which weighed three tonnes, was estimated to have been dead for about a week when found on Wednesday in the plantation in Aceh province, according to veterinarian from its Natural Resources Conservation Agency.

“There were no physical wounds, which may indicate either death by electricity or poison but to be sure it has to be based on a laboratory test,” Agus Aryanto, the agency's head, said by telephone.

Elephants frequently enter plantations in the area to feed on palm oil fruits, especially during the rainy season, he said, adding a team had this week been trying to prevent elephants straying onto human settlements.

World's most endangered animals Show all 17 1 /17 World's most endangered animals World's most endangered animals Amur Leopard Endemic to the far east of Russia, the Amur Leopard has a population of around 84 and is critically endangered. Here follows every species that the WWF lists as critically endangered. Getty World's most endangered animals Sumatran Elephant The Sumatran elephant population now stands at only 2400-2800 Getty World's most endangered animals Yangtze Finless Porpoise Endemic to China's Yangtze River, the Yangtze finless porpoise has an estimated population of 1000-1800 Kenichi Nobusue World's most endangered animals South China Tiger When discovered in the 1950s, the South China tiger population was estimated to be 4000, by 1996 it was estimated to be only 30-80. Scientists consider the tiger to be "functionally extinct" as one has not been sighted for over 25 years World's most endangered animals Sumatran Orangutan The Sumatran orangutan was once found across the island of Sumatra and even further south on Java. Today it is found only in the island's north and its population stands at 14,613 Getty World's most endangered animals Western Lowland Gorilla Though it is the most populous of all gorilla subspecies, the western lowland gorilla is still critically endangered and its population has declined by 60% in the last quarter century Getty World's most endangered animals Sumatran Rhinoceros The Sumatran rhinoceros is the smallest of the surviving rhinoceros species. Only 80 are known to be living today. The last male Sumatran rhino in Malaysia died on 28 May 2019 Willem V Strien World's most endangered animals Sumatran Tiger There are fewer than 400 Sumatran tigers left today. They are severely threatened by deforestation and poaching Getty World's most endangered animals Eastern Lowland Gorilla Half of the rainforest of the Democratic Republic of Congo in which these gorillas live has been destroyed the past 50 years. There were 17,000 Eastern Lowland gorillas in the 1990s but scientists estimate their population has declined by over 50% since then Getty World's most endangered animals Vaquita The world's rarest marine animal has a population of only 30. They were discovered in 1958 and are endemic to Mexico's Gulf of California Paula Olson / NOAA World's most endangered animals Javan Rhino The most threatened of all rhino species, there are only an estimated 58-68 Javan rhinos left Reuters World's most endangered animals Saola The saola was first sighted in 1992, being the first large mammal to be discovered in over 50 years. Scientists have only sighted saola in the wild four times and it is considered critically endangered World's most endangered animals Malayan Tiger The Malayan Tiger population now stands at only 250-300 Getty World's most endangered animals Hawksbill Turtle The population of the Hawksbill Turtle has declined by more than 80% in the last century. They are threatened by black market poachers who kill them for their shell Getty World's most endangered animals Black Rhino The population of the black rhino dropped by 98% in the years 1960-1995 due to poaching, it stands today at around 5000 Getty World's most endangered animals Cross River Gorilla The population of the Cross River gorilla has been damaged by deforestation and poaching, it now stands at 200-300 Julie Langford World's most endangered animals Bornean Orangutan The population of the Bornean orangutan has been reduced by over 50% in the past 60 years, now standing at around 104,700. Their habitat has been reduced by at least 50% in the 21st century Getty

Habitat loss and conflict with human have in recent years slashed the number of Sumatran elephants, which are found in tropical forests mainly on Sumatra and Borneo islands.

Another male Sumatran elephant was found decapitated and with its tusks removed in Riau province on Tuesday.

Elephant found in Riau province with its head and tusks removed (Reuters)

“Its tusks were cut off forcefully using a sharp tool,” said Heru Sutmantoro of the Natural Resources Conservation Agency in Riau. He said the elephant's separated head and trunk were lying close to the carcass.

Tests showed the 40-year-old elephant had no wounds and there was no indication of poisoning, he said.

Poaching and the illegal trade in wildlife remain rampant in Indonesia, despite efforts by authorities to crack down.

Under Indonesian law, poachers can be jailed for up to 10 years and fined up to 200 million rupiah (£11,000).

This year, a Russian man was detained at the airport on the island of Bali trying to smuggle a young orangutan in a suitcase.