One of the last casualties of Colombia's war with guerrillas have been the nation's indigenous tribes. Phil Rees went to the Amazon basin for the BBC's Newsnight to meet one group under threat.

It was a tiring, bumpy drive along unmade roads until we reached a ramshackle collection of small wooden shelters on the edge of the rainforest.

Suddenly a throng of half-naked children, some with pet monkeys on their shoulders, surrounded our jeep. They were smiling and shouting, asking for clean water, food or clothing.

My first reaction was of curiosity and wonderment. This makeshift camp was full of half of the world's remaining population of Nukak Indians; a tiny race of nomadic hunter-gatherers who live in northwest Amazonia. They have broad, sculptured faces with no eyebrows and little facial hair.

They decorate their faces with dye from berries. It is a culture where the monkey is both revered and eaten as part of a ritual of atonement with nature. It is a civilization largely untouched since the dawn of man.

My next reaction was of sadness. There were some 200 Nukak at the camp, sitting idly around unsure how to relate to the outside world. Eighty had arrived in late March from their jungle homes.

Before then, as nomads, they moved around at will, sleeping on hammocks constructed from giant palms. They hunt monkeys using blowpipes and poison darts and gather berries from the forest floor. If the men are skilled hunters, they can claim more than one wife.

Then, in March, one group stumbled on an arms cache, hidden in the dense undergrowth. The Nukak found themselves in the crossfire of Colombia's civil war. The arms belonged to the Revolutionary Armed Forces of Colombia (FARC), the Marxist guerrilla movement that has been staging a 40-year rebellion against the government in Bogotá.

The FARC became concerned that the Nukak could find more of their jungle hideaways and guide the army into their camps. FARC commanders ordered the group to leave the jungle.

"The Nukak's first knowledge of the outside world is from the sound of helicopters and bombs", said Dr. Javier Maldonado, a 27-year-old doctor who has been living and working with the tribe for 18 months. " They are a peaceful people and have no concept of war."

It is the Nukak's intimate knowledge of the jungle that has placed them in the battlefield. The Colombian security forces meanwhile tried to recruit them as scouts.

The remaining 200 Nukak are still in a distant jungle region controlled by the FARC and an understanding appears to have been reached, according to Dr Maldonado. The Nukak refer to any armed group simply as 'Green people', whether they are government soldiers, right-wing gunmen or leftist guerrillas.

"The Nukak get very frightened with the sound of helicopters and particularly bombs", said Dr Maldonado, who learnt the Nukak language and acted as my translator. Peape, one of the tribe who left the jungle in March, complained that white men make many guns; "They are the only ones who do these things", he said.

Once they are forced to leave the jungle, the Nukak begin to envy the outside world, believing its inhabitants posses a magical power. When they see a torch, they think its owners have harnessed the power of the sun. They watch planes overhead and believe they run on invisible roads constructed in the sky.

Most Nukak want clothes; one of the first things they learn from aid workers is to cover their bodies. One young teenage girl in the camp was given a wedding dress by a Christian charity and told that she should not walk around naked.

The first contact the Nukak made with the outside world was in 1988, when a group of about thirty Indians emerged from the jungle and walked into a town. They were naked and carrying blowpipes; the townspeople and the Indians stared at each other in disbelief.

This sudden collision of cultures has ravaged the Nukak. The Indians had no resistance to influenza. Initially, every member of the tribe over 40 died from the disease.

But now the war is a greater threat. At one time the tribe numbered over a thousand; barely 400 survive. The Colombian government is doing next to nothing to help; the aid is pitiful and there is no strategy on how to incorporate the Nukak into a world outside the jungle.

For thousands of years the Nukak had roamed the jungles of the upper Amazon basis, oblivious to the outside world. The United Nations warns that within little more than a generation, they could face extinction.

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