Six people are suspected of murdering a man and then eating him in a cannibalism ritual, EFE reported on Wednesday.
The victim was identified as Ocelio Alves de Carvalho, 21, and his remains were found near a village located some 1,200 km from Manaus, the capital of Amazonas state, the agency reported, quoting the news website G1.
The body bore no fewer than 60 knife wounds and was cut into pieces, according to a police official, who added that the man's heart, brain, liver and several other organs were not found.
According to the police, one witness said he had seen six people eating portions of the body, but the alleged killers have not been identified due to legal limitations.
The official said that the authorities had launched an investigation, but they were awaiting judicial authorisation to enter the Kulina reservation, which is protected by law.
"The law limits the work of the police, since it prevents entering the village to look for the suspects," he said.
Indigenous organisation Native Amazonia Operation, or Opan, said it did not know of any cases of cannibalism among the Kulina.
"It would be an unexpected deed, since such a case in that tribe has never been known," said Ivar Luiz Busatto, the coordinator of Opan, adding that "there are references to cannibalism in other tribes ... (but) for decades not a single case has been known of".