The US government is keen to get solid regional backing for its decision to spend $1.3bn on fighting drug trafficking and restoring peace to Colombia after decades of civil war.
Plan Colombia is a key topic for discussion between the US and South America.
The US government is keen to get solid regional backing for its decision to spend $1.3bn on fighting drug trafficking and restoring peace to Colombia after decades of civil war.
Some of Colombia´s neighbours, including Brazil, are far from enthusiastic.
Opposition parties in Brazil also say more military action against the drug traffickers inside Colombia could merely push the cocaine labs into Brazil.
Frontier platoons could find themselves having to cope with thousands of refugees.
Vast area
Brazil's Foreign Minister Luiz Felipe Lampreia has stressed the "autonomy" of Latin America's largest country, and has said it would not participate in Plan Colombia.
"We are concerned about Plan Colombia's possible effects on
Brazil, in terms of the military and in terms of drug
trafficking," he said.
"We have no intention of participating in any common international action."
The federal police do what they can to search all boats coming down river into Brazil.
But there are only six officers on duty at a time to cover a vast area and the border with Colombia stretches 1,000km north and is probably impossible to seal.
The US would like to see Brazilian soldiers join the federal police in blocking the flow of drugs and guns across the Brazilian/Colombian border and has offered Brazil $10m to sign up to Plan Colombia.
But Colonel Humberto Madeira of the army border patrol points out that the only serious incursion so far, came not from the FARC or the drug-traffickers, but from the Colombian army itself.
That is why his men have been strengthening their defences.
Though no one is saying it publicly, one strand of military thinking sees US military involvement in Amazonia as a bigger threat to Brazilian sovereignty than the Colombian conflict itself.