Venezuela and Ecuador sent troops to their borders with Colombia and downgraded diplomatic ties after their Andean neighbour bombed Colombian rebels inside Ecuador in an attack Caracas said could spark a war.
Escalating the worst dispute in the region for years, Venezuelan President Hugo Chavez deployed tanks to the frontier and mobilized warplanes, while President Rafael Correa bolstered Ecuador's military presence along the border.
Chavez ordered Venezuela's embassy in Bogota to be shut indefinitely from Monday and withdrew all of his diplomats.
Correa, a fellow leftist and close ally of the anti-U.S. Chavez, expelled Colombia's ambassador and recalled his own envoy in protest over what he said was a calculated violation of his small nation's sovereignty.
"May God spare us a war. But we are not going to allow them to violate our sovereign territory," Chavez, an ex-paratrooper said, warning he would attack Colombia with Russia-made jets if his neighbour carried out a raid in his OPEC country.
Colombia apologized to Ecuador for the troops crossing the frontier, but said the attack on a rebel camp was necessary after its forces came under fire from across the border.
But Colombia, a U.S. ally, also said it found documents at the jungle camp that linked the leftist government of Correa to the Marxist guerrillas - a charge Ecuador dismissed because the evidence was not presented for public scrutiny.
Colombia's troops killed on Saturday Raul Reyes, a leader of Marxist FARC rebels, during an attack that included air strikes and ground combat against a jungle camp in Ecuador in a severe blow to Latin America's oldest guerrilla insurgency.
Chavez and Correa said Colombian President Alvaro Uribe lied about the attack a few miles (kilometres) inside Ecuador.
Correa said planes bombed rebels from Ecuador's airspace while they slept and helicopters flew troops into the camp.
"This was a massacre ... We will not allow this to go unpunished," he said.
Venezuela's military went on alert "on land, in the air and at sea" and will support Ecuador "to the last", Chavez said.
Washington, which backs Uribe's fight against the rebels with its largest military aid outside the Middle East, said it was monitoring developments after Chavez's "odd reaction".
France, which has worked to free rebel-held hostages, called for restraint on all sides.
Political analysts said a conflict was unlikely because Chavez - the leader of Andean leftists - was more interested in firing up his base of support with rhetoric against Colombia. Despite his risky tactics, amid chronic food shortages he can ill afford to lose imports from Colombia, they added.
"We believe a military conflict between the two nations is unlikely at this stage but the growing political tension sets the stage for a potential overreaction to future events increasing the risk of costly miscalculations and missteps," Goldman Sachs economist Alberto Ramos said.
