Venezuela and Ecuador have moved troops to their respective borders with Colombia in a serious escalation of the worst crisis to hit the region for years. Both nations have frozen diplomatic ties with their neighbour in response to Colombia's killing of a left-wing guerrilla leader on Ecuadorean soil.
The incident has exposed the political fault lines in Latin America with Venezuela's President, Hugo Chavez, and his left-wing ally in Ecuador ranged against the US-backed Alvaro Uribe, the President of Colombia. Mr Chavez warned that any similar violation of its border by Colombia could spark a war.
Ecuador's President, Raphael Correa, said there could be "no justification" for the killing of Raul Reyes, thought to be the number two in Colombia's Farc rebellion, along with 16 other guerrillas in a bombing raid on Saturday.
In a further sign of hostilities, President Chavez's government said last night that it was expelling Colombia's ambassador and other diplomats from Venezuela.
Colombia accuses the Farc of using bases in Ecuador and Venezuela to launch attacks inside the country. Mr Uribe, whose father was kidnapped and killed by the guerrillas, has refused direct negotiations with the rebels and pursued a military solution, assisted by the largest US military aid budget outside the Middle East.
Fidel Castro, who retired as President of Cuba last month, voiced his support for Venezuela and Ecuador in an essay published in the Communist Party daily Granma. "We can plainly hear the trumpets of war to the south of our continent as a consequence of genocidal plans of the Yankee empire," Mr Castro wrote.
Regional analysts were surprised by Colombia's border incursion and said that while the escalation was largely posturing for domestic audiences, a conflict was possible. "This is an alarming degeneration in the region and has ominous overtones that could lead to provocative developments," said Larry Birns, director of the Council on Hemispheric Affairs, a Washington think-tank.
Venezuela's border with Colombia is already rife with drug and gun-runners, paramilitaries and guerrilla forces and the arrival of thousands more troops on both sides threatens to turn what has been a war of words into a shooting war. "There's no question of the enormous political tension now and any miscue could set off a conflict," said Michael Shifter, a vice-president of the Inter-American Dialogue group in Washington.
The Colombian raid, in which bombers were backed up by ground forces, has also complicated the fate of dozens of high-profile hostages, including Americans and a French citizen, held by the Farc.
France's Foreign Minister, Bernard Kouchner, expressed his dismay at the killing, saying that the dead rebel leader had been their contact in negotiations to free Ingrid Betancourt, a former Colombian presidential candidate who also holds French nationality.
"It is bad news that the man we were talking to, with whom we had contacts, has been killed," M. Kouchner told France Inter radio. Mme Betancourt has been held hostage in the Colombian jungle for six years. Mr Chavez has played a prominent role in the recent release of Farc hostages after offering to mediate between Bogota and the guerrillas. However, the two presidents fell out very publicly during the protracted negotiations.
The key figures
Charismatic commando turned politician who has used Venezuela's oil bonanza to start a "Bolivarian revolution". Critics call him a divisive firebrand; supporters say he is a champion of the poor.
Staunch US ally and right-wing populist who has won two commanding election victories in Colombia.
Uribe's hatred for Farc guerrillas stems from the death of his father.
Young left-wing economist and former minister who clinched a surprise win at the last Ecuadorean elections. Part of the so-called "pink tide" of socialist leaders in Latin America.Reuse content