Venezuela's president has told his armed forces to "prepare for war", saying a military pact between neighbouring Colombia and the US could set the stage for an invasion.
The comments by Hugo Chavez at the weekend were prompted by the presence of US troops gaining access to Colombian military bases.
Colombia has responded by saying it will protest to the UN security council and the Organisation of American States.
Chavez's comments also sparked clashes on Sunday on the Colombia-Venezuela border, where Colombians fought with Venezuelan border guards who responded by firing tear gas.
Chavez has said that US access to the Colombian bases poses a direct threat to his oil-exporting country.
But Washington and Bogota say the deal is aimed solely to create a joint force to fight drug cartels.