Bolivian President Evo Morales proposed that South Americans vote in a continent-wide referendum on Colombia's plan to give the US military greater access to its military bases.
Mr Morales said he will take the proposal to tomorrow's meeting of the Union of South American Nations, or Unasur, which will discuss negotiations between Bogota and Washington to allow increased US military presence at seven Colombian bases through a 10-year lease agreement.
"If the Colombian president wants his bases to be used, I say I want a referendum in South America so the people of Bolivia, Colombia, Peru, Venezuela, Brazil, Argentina - all 12 countries - can decide," said Mr Morales, who called the proposal a provocation by the US to create conflict and stall integration in the region.
The leftist governments in Venezuela and Ecuador also have criticised the pending deal, which the US says is necessary to help Colombia fight drug trafficking and leftist guerrillas.
Ecuador's national assembly passed a resolution on Tuesday saying the US use of Colombian military bases would undermine peace in the region.
Venezuelan President Hugo Chavez referred to the pending base deal as "a declaration of war against the Bolivarian Revolution," referring to his socialist political movement.
The Venezuelan leader said he had a right to speak to the Colombian people to deliver his Bolivarian message.
Yesterday, Colombia's ambassador to the Organisation of American States, Luis Alfonso Hoyos, protested to the hemispheric body that Mr Chavez was meddling in Colombia's internal affairs in violation of OAS principles.
Colombian officials deny the agreement is a threat to its neighbours, and say it is necessary to more effectively help Colombia's security forces fight drug traffickers and leftist rebels.