New concerns about "human safaris" are now being raised in Peru, where tour operators are profiting from the exploitation of indigenous tribes in the Amazon jungle.
An increase in economic activity and tourism in the Manu region has led to a dramatic rise in the number of reported sightings of the Mashco-Piro - one of around 15 indigenous groups in Peru who have no regular contact with outsiders, and one of only 100 or so such tribes left in the world.
Fenamad, the local indigenous rights organisation, has criticised tour operators who have taken advantage to take tourists "close to where" the tribespeople were seen.
There is growing evidence that travellers and tourists are attempting to make contact.
"Uncontacted Indians are not a tourist attraction," said Rebecca Spooner of Survival International, which aims to protect tribal peoples.
"So-called tour guides should already know better."
Growing concerns over "human safaris" caused a scandal in India after the Observer revealed how tour operators in the Andaman Islands were colluding with police to offer sightings of an indigenous group, the Jarawa, who have only had contact with the outside world since the late 1990s.
In Peru, the Mashco-Piro live in the Manu national park of the Madre de Dios region, near the Brazilian border. More than a century ago the Mashco-Piro were driven off their land in the upper Manu river by rubber tappers supplying the American and European car and bicycle industries. The tribe was forced to retreat to more remote jungle areas.
After Survival International published photographs of the tribe last month to publicise the need to leave it in peace, a spokesman for Peru's national protected areas department (Sernanp) urged people to steer clear of "communities trying to remain apart from the outside world". However, independent research has confirmed that unscrupulous tour guides are flouting that advice.
"The uncontacted peoples have been sighted on the Madre de Dios river in Manu. Let me know how many days you want and I'll suggest a tailor-made programme for your party," said one, contacted anonymously with a specific request to seek out the tribe.
"We can't be 100 per cent sure we can see the uncontacted. If we are lucky we can see. In 2011 they came out in the months of May and October," said another.
"The best time to see these uncontacted natives is towards the end of the dry season, when the turtles are laying their eggs along the riverbank," said a third operator. "The best chance you would have to see them is between July and September. Along the main rivers is the best place ..."
But other tour operators gave a markedly different response. Manu Nature Tours, based in Cuzco, said: "We do not offer any possibility to see [the tribe]. It is very dangerous to attempt any contact with them. A simple cold can kill them all. Any attempt to try to contact this people can put you in jail in Peru and Brazil."
Atalaya Tours said: "It is completely forbidden to contact 'non-contact people'. We have tours to Manu park, but Atalaya fully respects all the laws protecting non-contact natives and we don't agree with the illegal guides or operators that try to commercialise these kinds of visits."
According to Fenamad, "There's great concern because the Mashco-Piro are very vulnerable. In addition to their susceptibility to common diseases and epidemics, the sightings are occurring in an area of open-river transit where there is an intense traffic of commercial and tourists' boats."
Glenn Shepard, an anthropologist who has worked in Manu, says tour operators have approached the Mashco-Piro on the riverbank so that tourists can "get photos like they would for a jaguar".
Video footage of the Mashco-Piro emerged last year that appeared to show travellers "playing a game of cat and mouse with the naked tribesmen" and discussing whether to leave food or clothing for them on the riverbank.
None of the trips to Manu advertised by tour operators on their websites openly offers Mashco-Piro sightings, but several acknowledge the presence of "uncontacted" people in the rainforest.
"We need governments to act to protect indigenous communities, tour operators need to follow a code of conduct and tourists need to be educated and informed," said Mark Watson, director of Tourism Concern.