But Colombia presented photograph, videos and maps of what it said were Farc camps inside Venezuela.

'Sabre rattling'

Chavez, whose popularity has been slipping ahead of legislative elections in September, has cancelled a trip to Cuba, citing the danger of "armed aggression" by Colombia, and warned the US to stay out of the crisis.

"We have reports that 20,000 jobs have been lost because of this breaking of ties with Colombia"

Cesar Perez Vivas,
governor of Tachira

He has also threatened to cut off oil supplies to the United States if it backs a Colombian attack, although the US state department has said the US "has no intention of engaging in military action against Venezuela".

"Rather than posturing, it would be much more constructive for Venezuela to engage directly, answer these questions," Phillip Crowley, the US state department spokesman, said.

The US is the biggest buyer of oil from Venezuela, the fifth-largest supplier to the country.

Jose Vicente Carrasquero, a political analyst, told the AFP news agency, that Chavez was seeking to "excite the spirits of his supporters" ahead of the elections while simultaneously trying to "divert attention from the internal situation in Venezuela to a possible international conflict".

The parliamentary vote is the latest chance by opposition parties to gain a foothold in the country after being marginalised in 2005 legislative polls.

Dispute hurting business

Jose Rozo, the president of a business group in the border state of Tachira, said cross-border trade in several frontier towns had plunged by about 60 per cent in the past three days.

Bilateral trade with Colombia, once worth $7 billion a year, has plummeted since Chavez ordered a freeze on trade last year to protest a deal allowing US forces to use Colombian bases.

"A rise in troops levels on the border isn't justified; it is only hurting the residents here," Cesar Perez Vivas, the opposition governor of Tachira, said. 

"We have reports that 20,000 jobs have been lost because of this breaking of ties with Colombia."

Jorge Valero, Venezuela's ambassador to the UN, asked Ban Ki-moon, the UN secretary-general at a meeting on Monday to distribute a letter to the other UN member states which expresses hope that Juan Manuel Santos, Colombia's president-elect, does not follow "the warmongering plans" of the US government and outgoing President Alvaro Uribe.

The US on Friday threw its support behind Colombia, calling Chavez's severing of cross-border relations "a petulant response" to Bogota's accusations.