BY SHASTA DARLINGTON • SEPT. 10, 2017

SÃO PAULO, Brazil — They were members of an uncontacted tribe gathering eggs along the river in a remote part of the Amazon. Then, it appears, they had the bad luck of running into gold miners.

Now, federal prosecutors in Brazil have opened an investigation into the reported massacre of about 10 members of the tribe, the latest evidence that threats to endangered indigenous groups are on the rise in the country.

The Brazilian agency on indigenous affairs, Funai, said it had lodged a complaint with the prosecutor’s office in the state of Amazonas after the gold miners went to a bar near the border with Colombia, and bragged about the killings. They brandished a hand-carved paddle that they said had come from the tribe, the agency said.

“It was crude bar talk,” said Leila Silvia Burger Sotto-Maior, Funai’s coordinator for uncontacted and recently contacted tribes. “They even bragged about cutting up the bodies and throwing them in the river.”

The miners, she said, claimed that “they had to kill them or be killed.”

Ms. Sotto-Maior said the killings were reported to have taken place last month. The indigenous affairs bureau conducted some initial interviews in the town and then took the case to the police.

“There is a lot of evidence, but it needs to be proven,” she said.

The prosecutor in charge of the case, Pablo Luz de Beltrand, confirmed that an investigation had begun, but said he could not discuss the details of the case while it was underway. He said the episode was alleged to have occurred in the Javari Valley — the second-largest indigenous reserve in Brazil — in the remote west.

“We are following up, but the territories are big and access is limited,” Mr. Beltrand said. “These tribes are uncontacted — even Funai has only sporadic information about them. So it’s difficult work that requires all government departments working together.”

Mr. Beltrand said it was the second such episode that he was investigating this year. The first reported killing of uncontacted indigenous people in the region occurred in February, and that case is still open. “It was the first time that we’d had this kind of case in this region,” he said in a telephone interview. “It’s not something that was happening before.”

Survival International, a global indigenous rights group, warned that given the small sizes of the uncontacted Amazon tribes, this latest episode could mean that a significant percentage of a remote ethnic group was wiped out.

“If the investigation confirms the reports, it will be yet another genocidal massacre resulting directly from the Brazilian government’s failure to protect isolated tribes — something that is guaranteed in the Constitution,” said Sarah Shenker, a senior campaigner with the rights group.

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