By Jeremy McDermott
BBC News, Medellin
Colombian President Alvaro Uribe has given rebels an ultimatum - release more than 60 hostages or see a guerrilla leader extradited to the US.
Palmera is the most senior Farc rebel in captivity
Ricardo Palmera, better known by his alias Simon Trinidad, is the most senior commander of Revolutionary Armed Forces of Colombia (Farc) in captivity.
He is wanted in the US on kidnapping and drugs trafficking charges.
The Farc have been collecting hostages - politicians, security operatives, and three intelligence contractors.
The rebels have said they will not be released until hundreds of Farc guerrillas in prison are freed.
But in an unprecedented move, President Alvaro Uribe has turned the tables on the guerrillas, using their own tactics against them.
He holds in prison Simon Trinidad, one of the Farc negotiators during a failed peace process with the last government.
The president has given the Farc until 30 December to release the 63 political hostages they hold, or else Trinidad will be extradited to the US to face kidnapping and drugs trafficking charges.