Venezuelan soldiers blew up two makeshift foot bridges that stretched across the border to Colombia in the latest incident to stoke a diplomatic dispute between the Andean neighbours.

Colombia's government criticized the destruction of the bridges as an aggression and a violation of international law, which it would denounce at the United Nations and the Organization of American States in Washington.

The long-simmering Andes spat has been mostly limited to diplomatic barbs in the past. But the current crisis is raising the risk of more violence along the volatile frontier where rebels, drug gangs and smugglers operate.

General Eusebio Aguero, Venezuela's army commander in the Tachira border region, ordered his soldiers to destroy the bridges using explosives. He said the crossings were unauthorized and used for illegal activities.

"They are two foot bridges that paramilitary fighters used, where gasoline and drug precursors were smuggled, subversive groups entered," he told reporters, adding that several other bridges would be destroyed. "They are not considered in any international treaty."

Colombian Defence Minister Gabriel Silva said troops from the Venezuelan army arrived in trucks and dynamited the bridges that cross into Colombia's Norte de Santander department.

The Colombian Foreign Ministry said in a statement: "This is a unilateral act and an aggression against the civilian population and the frontier communities."

MORE ACCESS FOR U.S. MILITARY

Tensions are high between US ally Colombia and Venezuela over a Colombian plan to allow the United States more access to its military bases as part of anti-drug and counter-insurgency cooperation against FARC rebels.

Venezuela's President Hugo Chávez, a fierce US adversary, has sent more troops to the border and told his military commanders to "prepare for war" because he says the US base plan could be used to stage an invasion of his OPEC nation.

In a document to justify a request for funds to expand one of the bases, the US Air Force said Colombia was ideal to provide air access to most of South America and cited anti-US governments as one of the reasons it needed that access.

Colombian President Alvaro Uribe says the base deal is just an extension of current cooperation with US troops. But he has urged the United Nations and the Organization of American States to investigate Chávez's "war threats".

The two countries have in the past managed to work out their differences. But the current crisis is already cutting into their $7 billion annual bilateral trade, making this dispute harder to resolve.

Many analysts say Chávez may be looking for political gain by stirring up tensions as a way to distract from domestic troubles, such as power and water shortages that are threatening to dent his popularity.

Colombia's four-decade guerrilla war often spills over the border, where killing and kidnapping are common. Chávez accuses Colombia of not protecting its border, while Colombian officials say he backs Colombia's FARC rebels.