JAKARTA (AFP) - Two Indonesian men arrested for shooting an orang utan multiple times and then decapitating it before tossing the corpse into a river have told investigators they acted in self-defence, police said on Thursday (Feb 1).

The suspects, both rubber plantation workers on the island of Borneo, admitted they killed the critically endangered male Bornean orang utan, whose headless body was found last month.

Its hair was burned off its body, which was riddled with at least 17 bullet wounds.

Pictures of the beheaded corpse floating by the riverbank quickly spread online and sparked an angry reaction from animal rights activists, among others.

"They claimed they killed the orang utan because they were scared to see such a big animal suddenly coming their way," Central Borneo police chief Anang Revandoko said.

"The investigation is still ongoing," he added.

Orang utans can grow to the size of humans and have enormously powerful arms, but are not known to attack unless their habitat is threatened.

Investigators said they seized a machete allegedly used to attack the animal, whose body was discovered by a local villager.

"The men shot the animal multiple times, but (they said) it didn't die," police chief Revandoko said.

"One of them then decapitated it from behind. Then they buried its head in the backyard of their house and dumped the body in the river."

If convicted, the suspects, who are 32 and 41, could face up to five years in jail under Indonesia's conservation law, he added.

Bornean and Sumatran orang utans are listed as critically endangered by the International Union for Conservation of Nature (IUCN).

The Sumatran orang utan population is estimated to be just under 15,000, while about 54,000 orang utans are thought to live in Borneo, according to the IUCN.

Rampant logging and the rapid expansion of palm oil plantations have been blamed for destroying their jungle habitat.

Plantation workers and villagers are sometimes known to attack an animal that many see as a pest, while poachers also capture them to sell as pets.