Several South American leaders have criticised US plans to deploy extra troops at bases in Colombia, accusing Washington of using the war on drugs as a pretext to boost its regional military presence.
Colombian President Alvaro Uribe is meeting South American leaders this week to try to generate support for the US plan to base anti-drug flights in the world's top cocaine producer after the US military lost access to a base in neighbouring Ecuador.
Venezuelan President Hugo Chavez - a persistent critic of Washington - said the Colombian plan could be a step towards war in South America and called on President Barack Obama not to increase the US military presence in Colombia.
"These bases could be the start of a war in South America," the socialist Chavez told reporters. "We're talking about the Yankees, the most aggressive nation in human history."
Mr Chavez, who has put his troops on alert in previous diplomatic disputes with Colombia, ratcheted up the spat with Bogota by barring Colombian state-run energy firm Ecopetrol from the Orinoco oil region and said imports of some 10,000 vehicles would be halted.
A close Chavez ally, Bolivian President Evo Morales, a former coca farmer who ousted US anti-drug agents last year, said Colombia's drug-funded Farc rebels had become Washington's "best tool" to justify military operations in the region.
"We can't have all these planes and military equipment concentrated in Colombia. This is against the Farc. This isn't against drug-trafficking, it's against the region. Our duty is to reject it," said Mr Morales, who met President Uribe on Tuesday.
Mr Uribe's security drive would give US forces access to seven Colombian bases and increase the number of American troops in the Andean nation above the current total of less than 300 but not more than 800, the maximum permitted under an existing pact.
The uproar could spoil President Obama's efforts to improve ties with Latin America while carrying on the war on drugs, which critics say has failed.
Mr Obama won praise for condemning a military coup in June that ousted Honduras' left-wing president, but some have faulted him for not taking a more active role in talks to reinstate the deposed leader, Manuel Zelaya.
The Colombian president, who is deciding whether to run for a third term, has tense relations with Ecuador and Venezuela and is not visiting their leaders on his tour.
Colombia has clashed with both neighbours on several occasions after the government's battle against rebels from the Revolutionary Armed Forces of Colombia, known as Farc, spilt across its borders.
The guerrilla army is funded by the cocaine trade and has fought an insurgency against the state for 45 years.
Mr Chavez last week withdrew his diplomats from Bogota after the Colombian government said weapons bought by Venezuela in Sweden had made their way to the Farc.
Reuters