A FEW hours north of Bolivia's capital of La Paz, a nearly impassable dirt road runs along the edge of cliffs covered in a thick jungle canopy. It is difficult to imagine that this little-known Yungas region has become South America's latest drugs battlefront, bringing the United States and Bolivia on to a collision course.
Bolivian coca cultivation is still associated with the southern Bolivian Chapare region, which provided the basic ingredient for almost half the world's cocaine during the 1980s and 1990s. After decades of looking the other way, the Bolivian government, with the help of millions of dollars of US military aid, launched the Dignity Plan in 1998, almost eliminating Chapare's coca production by 2001.
Since then Yungas, an almost inaccessible area, has become the country's main coca-growing area. The government allows 12,000 hectares of legal coca cultivation in Yungas, but real production is nearly double that and growing - explaining the 35 per cent increase in cocaine production last year from 2003, according to the latest UN World Drug Report, and consolidating Bolivia as the world's third-largest cocaine producer.
The US now seems determined to put an end to this situation, despite stern opposition from Evo Morales - a leader of the Chapare coca growers and favourite to win next Sunday's presidential elections - who defends the legalisation of coca for traditional uses such as medicinal tea.
A senior member of Mr Morales's party said the American embassy had told them Yungas was one issue the US would stand firm on. The US ambassador to Bolivia, David Greenlee, warned that Mr Morales' idea of legalising coca would have repercussions.
But Mr Morales refuses to budge. "We'll have zero cocaine but not zero coca," he told The Scotsman. "The US isn't really interested in cocaine eradication - it uses the war against drugs like the war against terror in Iraq, as an excuse to dominate other countries.
"The fact that it doesn't really target the demand for drugs demonstrates this."
Influential members of Mr Morales' party are even pushing to expel US anti-narcotics police from Bolivia.
In the midst of the growing US-Morales power struggle stand impoverished Bolivian peasants such as Antonio Florencio, 34, a father of four who cultivates a small, steep patch of coca land near Coroico, a town in the heart of Yungas.
"I used to grow coffee, but couldn't maintain my children so I decided to move here seven years ago," he said. "But it's a very hard life, we barely make enough money to survive."
If Mr Morales wins the election, Bolivia could feel the full force of US wrath, but with so few allies in the region, the Bush administration will have to think long and hard about how to act on its displeasure.