Meet the Mascho-Piro tribe of Peru ... but do they want to meet the modern world?

They've no idea what to make of the strange people who have appeared on the far riverbank, wearing clothes, carrying cameras, and using alien transportation devices. But they are right to be concerned.

The men and women captured in the photographs belong to the Mascho-Piro, one of the world's last uncontacted tribes. For a millenia, they have carved an existence from the Peruvian rainforest, untouched by what outsiders call civilisation.

Now their days of isolation seem numbered. Illegal loggers are encroaching nearer to their ancestral homeland, in and around Manú National Park in the largely unexplored region where Peru borders Brazil and Bolivia.

The family in our main photo were chanced upon by Diego Cortijo, an indigenous Peruvian exploring the Alto Madre de Dios river four days on foot from the remote jungle town of Puerto Maldonado.

Holding his camera lens against a telescope, he captured one of the most detailed pictures of an uncontacted tribe ever taken. It appears to show a family gazing at him with a mixture of fear and hostility.

The second image was taken by Gabriella Galli, an Italian visitor on a bird-watching tour of the national park. She was taking a speedboat down the Alto Madre de Dios, a tributary of the Amazon, when she spotted humans on the far bank. Concerned a tourist could come so close to uncontacted tribes, Ms Gali passed her photograph to Survival International, which fights for the protection of indigenous people.

So-called "first contact" with the outside world can prove fatal for a tribe and usually results in the death of between 50 and 80 per cent of its members, who have no immunity to diseases common elsewhere.

It can also be tragic for those who "discover" them. Weeks ago, a close friend of Mr Cortijo – Nicolás "Shaco" Flores – was killed by an arrow on the outskirts of the park while trying to leave gifts of food and clothes.

"Shaco's death is a tragedy: he was a kind, courageous and knowledgeable man," wrote anthropologist Glen Shephard, a friend of the victim, on his blog. "Yet in this tragic incident, the Mashco-Piro have again expressed their adamant desire to be left alone."