By James Ingham
BBC News, Caracas
Strikes on Farc rebels outside Colombia threaten regional stability
Venezuela's decision to deploy troops and tanks to the Colombian border has plunged relations between the two countries to a new and worrying low.
The decision was made in response to Saturday's killing of a Farc rebel leader in an air and ground operation near Colombia's southern border - but just inside Ecuador.
Despite President Hugo Chavez saying he does not want war, his tough response to the killing has made the threat of conflict very real.
"Mr Defence Minister, move me ten battalions of tanks to the border immediately," said Mr Chavez on Sunday, making the bold instruction live during his weekly televised broadcast to the nation.
"We are not going to permit the North American empire and its puppy President Uribe and the Colombian oligarchy to divide us, to come here and make us weak," he said.
Mr Chavez said he was taking such measures as a warning to his neighbour to consider carefully any military activity in Venezuela in its pursuit of Farc rebels.
"President Uribe, think about it long and hard," he said.
"You had better not get the idea of doing this in our territory because it would be cause for a war."
It is Mr Chavez's involvement in the Colombian conflict that has increased tension between the two presidents and bought relations between Colombia and Venezuela to an all-time low.
Mr Uribe has promised the Colombian people he will take a tough stance against the guerrilla movement that for more than 40 years has used kidnapping and murder as a weapon against the state. He believes they can be stopped militarily.
Mr Chavez, on the other hand, has offered his support to the Marxist rebels.
While not endorsing their methods, he has said Farc should be treated as an insurgent force rather than as terrorists, claiming they have a legitimate political goal.
But anecdotal evidence points to more tacit support.
Former rebels who have defected have spoken of receiving co-operation from some in the Venezuelan military.
They have also reported that Venezuela has provided weapons, shelter and financial support.
Venezuela's main opposition leader, Manuel Rosales, has often spoken out about these links.
"The guerrillas go in and out of our national territory, kidnap people and make alliances with criminals, who they train in kidnapping and extortion," he said recently.
Relations between the two countries were not always so bad.
Last year, Mr Chavez was a part of official negotiations between Farc and the Colombian government.
There were high hopes then that his involvement would lead to some kind of settlement centred around Farc's proposal to release high-profile hostages in return for its members serving time in Colombian jails.
But Mr Chavez was shortly afterwards dismissed from his role by Mr Uribe, who accused him of breaking an agreement he had made not to speak to the Colombian Army.
Angry words were exchanged between the two, but Mr Chavez maintained contact with Farc which later resulted in the release of six hostages to Venezuela.
That was seen by many as a significant breakthrough. Families of hostages still being held hoped it would lead to renewed negotiations.
But Saturday's attack, just three days after four hostages were freed, would appear to rule that out.
So what of the military build up on the Venezuelan side of the border - is this just blustering from President Chavez or would he really be prepared to use force against Colombia?
Some analysts doubt he would invade his neighbour.
"Venezuela is too dependent on food exports from Colombia," said Liliana Fasciani, a legal philosophy professor at the Andres Bello Catholic University in Caracas.
"And the Colombian military's superior training make a wide-scale war unlikely."
But Mr Chavez's supporters see no problem with the threat.
Many share a similar feeling that Colombia is being used by the United States, keen to keep a foothold in South America.
Isolation or acceptance
Heinz Dieterich, a political analyst from Mexico's Metropolitan University and one of Mr Chavez's advisors, said Latin American countries have only two options.
Mr Chavez claims Farc rebels have a legitimate political goal
"They either diplomatically isolate Bogota or together accept the Colombian guerrillas as a belligerent force," said Mr Dieterich.
"This is the only way of defending their interests and those of the popular democratic forces against the imperial axis of Washington and Bogota."
As tanks prepare to move from bases around the country and fighter jets sit ready at air bases, other countries are rushing to try to avoid a deepening of the crisis.
Peru, Chile and Argentina have all expressed concern about the weekend's escalation.
Whether sharing similar sympathies towards Farc or not, all seem concerned about Colombia's incursion into a neighbouring country.
An emergency meeting of the Organisation of American States will be held as the continent tries to quell the deep diplomatic tension - a tension that Mr Chavez has said could lead to war.