By Gary Duffy
BBC News, Sao Paulo
Coca plantations and a fully-equipped laboratory for making cocaine have been found for the first time in a Brazilian part of the Amazon rainforest.
Coca is usually grown in countries neighbouring Brazil
A senior army officer said the find might mean drug traffickers were trying to find new locations to grow coca.
The authorities would need to stay on alert, he said.
The leaf, a key ingredient of cocaine, is normally grown in mountainous regions in some of Brazil's neighbours such as Bolivia, Peru and Colombia.
The authorities in Brazil say it was satellite images of a large area of Amazon rainforest that had been cleared which first attracted their attention.
In total, four plantations were discovered covering an area of between 100 and 150 hectares, according to the government news agency Agencia Brasil.
The army and police used small boats and three helicopters to reach the area, which is near to the north western city of Tabatinga, close to the border with Peru and Colombia.
The coca, which was almost ready for harvest, was found along with a fully equipped laboratory prepared to manufacture cocaine.
No-one was arrested, but the coca was destroyed.
The army says it is the first time that plantations like this have been discovered in the Brazilian Amazon, where the climate was not thought to favour coca fields.
A different plant known as epadu, which can also be used to produce cocaine, is more common in the area, but is much less productive.
The army believes drug traffickers may be trying to adapt or genetically modify the coca leaf and find new locations for plantations.
A senior officer warned that if there was not an immediate crackdown, it might even become a new source of deforestation.
Walter Maierovitch, who used to lead Brazil's effort to combat drugs, has described the discovery as "worrying", and a possible indication that some Colombian drug cartels were changing their strategy.
Soldiers are remaining in the area to try to find those behind the plantations, and to check for other possible locations which might have been used by the drug traffickers.