Fears of a conflict involving Colombia, Ecuador and Venezuela have increased after Colombian troops killed 17 people during a raid into Ecuador.
Venezuela and Ecuador withdrew their ambassadors from Bogota and sent troops to the border after Colombian troops killed a Farc leader, Raul Reyes, and 16 other rebels during a raid into Ecuador.
Colombia has claimed it has evidence of links between left-wing Farc guerrillas and Ecuador President Rafael Correa.
Mr Correa said Colombia deliberately carried out the strike beyond its borders and that there was no justification for it. He snubbed an earlier announcement from Colombia that it would apologise for the incursion.
Colombian officials have long complained that Ecuador's military does not control its sparsely populated border, allowing rebels to take refuge.
President Correa said the rebels were "bombed and massacred as they slept, using precision technology." He said Colombia violated Ecuador's airspace when it bombed the rebel camp, which the Colombian military said was located 1.1 miles from the border.
Venezuela President Hugo Chavez ordered tanks and troops to the border with Colombia, accusing it of pushing South America to the brink of war by its actions.
Mr Chavez said Venezuela would respond militarily if Colombia violates its border. "We don't want war, but we aren't going to permit the US empire, which is the master (of Colombia) . . . to come divide us," he said.
President Chavez called Colombian President Alvaro Uribe "a criminal" and branded his government a "terrorist state," likening it to Israel for its US-backed attacks on militants.