A critically endangered Bornean orangutan has been shot dead, hacked to pieces and eaten by workers after straying onto an Indonesian palm oil plantation, police and activists said Thursday.

Police have formally named three male suspects in the brutal killing in Kapuas Hulu district, in the Indonesian part of Borneo island, while another seven are being questioned as witnesses to the crime.

Authorities launched an investigation after media ran stories showing gruesome pictures of the slaughtered ape.

The workers were detained after police found orangutan bones and dried meat in a cupboard at a plantation workers' camp, in a remote part of the jungle-clad island, local police chief Jukiman Situmorang told AFP.

He said the three workers named as suspects stand accused of "shooting, hacking, chopping, cooking and eating the orangutan" on January 27. The men could be jailed for up to five years if found guilty of breaking laws that protect the animals.

Environmental group the Centre for Orangutan Protection (COP) condemned the killing and urged police to target the company that runs the plantation as well as the workers.

The head of COP, Hardi Baktiantoro, criticised palm oil companies for introducing rules that see workers punished if there is any damage to plants.

This means they view orangutans, who often stray onto plantations accidentally and cause damage, as pests and attack them.

He also said authorities should never have given permission for a plantation in the area: "Why would they give a permit in an area that is an orangutan habitat?"

The rapid expansion of palm oil plantations on Borneo has been blamed for destroying orangutans' natural jungle habitat. They are also attacked by villagers who view them as pests and targeted by poachers to be sold as pets.

The habitat of Bornean orangutans has dwindled by over 50 percent in the past 20 years, and its population has fallen by more than 50 percent over the past 60 years, according to the WWF.

The International Union for Conservation of Nature classifies the animal as critically endangered.