Hundreds of Venezuelan troops today began leaving for the country's border with Colombia ahead of emergency talks aimed at preventing an increasingly tense regional standoff from descending into armed conflict.
Officers said soldiers seen boarding buses and trucks in the central city of Valencia were heading south towards the Colombian border.
The US president, George Bush, accused the Venezuelan president, Hugo Chávez, and his government of "provocative manoeuvres" against Colombia, vowing to oppose any act of aggression in the Andean region.
"I told him that America would continue to stand with Colombia," Bush told reporters.
The troop movements were ordered by Chávez on Sunday in response to a controversial Colombian military operation the day before.
Colombia's military launched an air raid on a camp belonging to the Revolutionary Armed Forces of Colombia (Farc) group a mile inside Ecuador, killing 17 rebels including Raúl Reyes, a senior Farc commander.
Ecuador responded by cutting diplomatic links with Colombia and sending 3,200 troops to the border between the countries.
Although the crisis originally involved Colombia and Ecuador, it has become dominated by an increasingly bitter war of words between Colombia and Venezuela, and especially their ideologically divided presidents, the pro-US rightwinger Alvaro Uribe and Chávez, the self-styled scourge of Washington in the region.
Today, a Venezuelan government minister and key Chávez ally was reported as saying the country's border with Colombia had been sealed.
The government had "taken some measures … like closing the border", news agencies quoted the agriculture minister, Elia Jaua, as having told the Colombian television station Caracol.
While there were reports of Colombian vehicles being turned back at border crossings, elsewhere the frontier – a crucial trade access point for Venezuela, especially for food imports – remained open.
Regional analysts believe war is very unlikely, noting that Venezuela's military would not relish taking on Colombian forces well equipped with modern US weaponry. However, fears remained that skirmishes could break out in isolated border regions.
Members of the Organisation of American States (OAS), Latin America's main regional forum, are to meet in an attempt to ease tensions.
The OAS hoped to provide "guidance permitting [the nations] to reach a peaceful solution to this crisis", the organisation's general secretary, José Miguel Insulza, said.
In a television address on Sunday, Chávez lambasted his Colombian counterpart as a "criminal" and "lackey" of the US.
The Colombian response has been equally vehement. The country's government says documents recovered from a laptop belonging to Reyes showed the Chávez government gave the rebel group - which the US and EU consider to be a terrorist organisation - $300m (£150m) in funding.
Such support for Farc meant Chávez should be tried by the international criminal court, Uribe said today.
In a further dramatic development, Uribe's vice-president, Francisco Santos, told a UN disarmament forum in Geneva today that the Farc documents also revealed the group was seeking to acquire uranium to build a radioactive "dirty bomb".
Santos presented no evidence to back up the claim. Analysts said that, even if Farc had the ambition to obtain radioactive material, it was very unlikely to have got far with such a plan.
Colombia has faced criticism from countries including Brazil, Chile and Nicaragua, with an ailing Fidel Castro also joining in.
The Ecuadorean president, Rafael Correa, said Colombia's raid had brought an end to talks between his government and Farc guerrillas to free 12 hostages, including the French-Colombian politician Ingrid Betancourt and three US nationals.
In a statement today, Farc said the raid had severely damaged chances of a deal to release the hostages.
The group, which has been waging a decades-long insurgency against the Colombian state, is thought to fund its 11,000-strong armed force through drugs and kidnapping.
