There are other levers too: several AUC leaders could still be extradited to the United States on drugs charges if they fail to toe the line.The United States has given Colombia some $3.5 billion in military aid since 2000.
But there are signs that the government might be prepared to agree not to extradite AUC leaders in return for a peace deal.The United States, which provides Colombia with some $500m a year in military aid, has other ideas.
Although this seemed the president's best chance of a peace deal before he leaves office next summer, negotiations have failed to get off the ground in the face of fierce opposition from the right-wing paramilitaries of the United Self-Defence Forces of Colombia (AUC).
The site proposed for the enclave was once an ELN stronghold, but the guerrillas were driven out of much of the area by the right-wing paramilitaries of the United Self-Defence Forces of Colombia (AUC).
But neither the United States government nor the Colombian government is fooled, says one American counter-narcotics official: "These are drug traffickers, who are trying everything they can to find the open window".The newest AUC converts appear to be taking advantage of the safe haven in Santa Fe de Ralito, a village in north-western Colombia.
The battle for the town involved large forces (1,000 FARC and 600 AUC, according to one report), and lasted three days.
One is what will happen to areas under AUC control if peace talks, due to begin on July 1st, prosper.
On July 28th it was the turn of three warlords from a much larger force of right-wing paramilitary vigilantes, the United Self-Defence Forces of Colombia (AUC).
Mr Castaño had been pushing hard for a deal: he was said to be prepared to plea-bargain with the United States, and to accept that AUC leaders would have to serve some jail time.
But until the entire AUC has been demobilised, all paramilitaries are barred from politics.This has not stopped the AUC from continuing to work behind the scenes.
The FARC and, especially, the AUC have close links to the drug trade; human-rights groups accuse the army of aiding the AUC, though other analysts say that such links are the exception rather than the rule.
