IF YOU massacre members of one of the world’s last remaining uncontacted tribes, it’s really not a smart idea to brag about it at a bar — but that’s exactly what a pair of illegal goldminers in Brazil are alleged to have done.

Public prosecutors in Brazil have opened an investigation after reports that illegal goldminers along a remote Amazon river killed between 10 and 20 members of a famous uncontacted tribe. Two miners have reportedly been arrested.

Federal police and the Public Prosecutor’s office are investigating the killings of an unspecified number of indigenous people on the border with Peru and Colombia.

The investigation was launched after the gold miners were heard bragging about the killings in a bar. The miners reportedly brandished a hand-carved paddle they claimed was taken from the indigenous tribe.

Leila Silvia Burger Sotto-Maior works for the Brazilian agency on indigenous affairs and is the department’s co-ordinator for uncontacted and recently contacted tribes. Her agency lodged a complaint with the prosecutor’s office after learning about the men bragging about the killings while drinking.

“It was crude bar talk,” she told The New York Times.

“They even bragged about cutting up the bodies and throwing them in the river.”

The killings allegedly took place last month with the miners claiming “they had to kill them or be killed,” Ms Sotto-Maior said.

Investigators say the bodies were cut up so they wouldn’t float and dumped in the river. “There is a lot of evidence, but it needs to be proven,” she said.

Illegal miners represent one of the most pressing threats to the uncontacted peoples in the Amazon and have been blamed for introducing new diseases and polluting the rivers and forest. Last year the Peru government declared an emergency because of mercury contamination caused by illegal gold mining in the Amazon.

Fiona Watson is the Campaigns Director at Survival International, a global indigenous rights group dedicated to protecting the rights of tribal communities that remain largely cut off from the outside world.

“Not very long ago, many denied the existence of uncontacted tribes and claimed they could invade their land with impunity,” she told news.com.au in December.

“We give tribal peoples with experience of contact a platform to speak to the world, and raise awareness of this urgent and horrific humanitarian crisis.”

According to Survival International, given the small size of these uncontacted Amazon tribes, this latest episode could mean a significant percentage of a remote ethnic group was wiped out. If 10 indigenous tribespeople are confirmed to have been killed, that could represent 20 per cent of the tribe, the group says.

Brazilian President Michel Temer has come under fire over the alleged massacre as well as other reports of indigenous killings in Brazil this year.

Prosecutors are also investigating another complaint about the alleged killing of indigenous people from the isolated Warikama Djapar tribe. The attack is thought to have occurred in May but has not been confirmed.

“If these reports are confirmed, President Temer and his government bear a heavy responsibility for this genocidal attack,” Survival International Director Stephen Corry said in a statement.

“All these tribes should have had their lands properly recognised and protected years ago — the government’s open support for those who want to open up indigenous territories is utterly shameful, and is setting indigenous rights in Brazil back decades.”

President Temer’s government has faced international criticism after neglecting environmental and indigenous rights issues amid an economic crisis. Several government groups tasked with protecting uncontacted indigenous territories have recently had their funding slashed by the Brazilian government and have had to close down.