Brazil's National Indian Foundation has confirmed Brazil's last uncontacted Indian tribes has been spotted in the far western Amazon jungle near the Peruvian border.
The Indians were sighted in an Ethno-Environmental Protected Area along the Envira River in flights over remote Acre state, said the government foundation, known as Funai.
"Four distinct isolated peoples exist in this region, whom we have accompanied for 20 years," Funai expert Jose Carlos Meirelles Junior said in a statement.
Funai does not make contact with the Indians and prevents invasions of their land, to ensure "total autonomy" for the isolated tribes.
Survival International said the Indians were in danger from illegal logging in Peru, which is driving uncontacted tribes over the border and could lead to conflict with the estimated 500 uncontacted Indians now living on the Brazilian side.
There are more than 100 uncontacted tribes worldwide, most of them in Brazil and Peru, the group said in a statement.
"These pictures are further evidence that uncontacted tribes really do exist," Survival director Stephen Corry said.
"The world needs to wake up to this and ensure that their territory is protected in accordance with international law. Otherwise, they will soon be made extinct."
The Daily Mail reported the tribsemen responded with aggression to the aircraft flying overhead:
"Skin painted bright red, heads partially shaved, arrows drawn back in the longbows and aimed square at the aircraft buzzing overhead. The gesture is unmistakable: Stay Away," the report said.
"Behind the two men stands another figure, possibly a woman, her stance also seemingly defiant. Her skin painted dark, nearly black.
"The apparent aggression shown by these people is quite understandable. For they are members of one of Earth's last uncontacted tribes, who live in the Envira region in the thick rainforest along the Brazilian-Peruvian frontier.
"Thought never to have had any contact with the outside world, everything about these people is, and hopefully will remain, a mystery.
Their extraordinary body paint, precisely what they eat (the anthropologists saw evidence of gardens from the air), how they construct their tent-like camp, their language, how their society operates - the life of these Amerindians remains a mystery.
Meirelles said the flight was made for scientific reasons, not to disturb the tribe.
"We did the overflight to show their houses, to show they are there, to show they exist," he said. "This is very important because there are some who doubt their existence."
Meirelles, who despite once being shot in the shoulder by an arrow fired by another tribe campaigns to protect these peoples, believes this group's numbers are increasing, and pointed out how strong and healthy the people seemed.