The Revolutionary Armed Forces of Colombia (Farc) have said the Colombian government must withdraw its forces from two southern towns before there can be progress on a proposed prisoner swap.
The rebels made military withdrawal a condition on Tuesday after Alvaro Uribe, Colombia's president, said he would re-start talks with the group.
Raul Reyes, a Farc commander and spokesman, was quoted on a pro-Farc website as saying: "We'll begin to believe in the option of a humanitarian exchange the day the president orders the withdrawal of security forces from the towns of Florida and Pradera."
The two towns in southwestern Colombia are likely to be the location for talks aimed at freeing some 60 people taken prisoner by Farc, including three American defence contractors.
Reyes said: "Without this prerequisite, whatever the president says is nothing more than demagoguery, stalling, deception and a lack of respect to the family members, individuals and countries who are promoting this potential agreement."
Uribe broke off contact with Farc in October, blaming the group for a car bombing that injured 23 people at a military university in Bogota, the capital.
He has since re-authorised European diplomats to begin talks with Farc over the proposed prisoner exchange.
Uribe has said that France, Spain and Switzerland, the three European peace facilitators, should provide military rather than diplomatic assistance to guarantee the release of the prisoners.
Among those held by Farc is Ingrid Betancourt, a politician and anti-corruption activist with French citizenship, who was kidnapped in February 2002 while campaigning for the Colombian presidency.