Colombia's Farc rebels have demanded that government forces clear out of two mountain areas before talks on hostage releases can take place there.
Farc rebels want senior leaders released
The government immediately rejected the demand, accusing the rebels of closing the door on dialogue.
Hopes that about 63 hostages might soon be freed sank on the news. Some have been held hostage since 2002.
The captives include three US military contractors and the French-Colombian politician Ingrid Betancourt.
In a letter the Farc said it wanted two municipalities to be demilitarised in order for the negotiations to take place.
"Without this guarantee... it would be useless," the statement said.
It said it would be willing to release about 60 hostages in a prisoner exchange, but demanded that two guerrilla commanders - Ricardo Palmera and Nayibe Rojas, both recently extradited to the United States on drug charges - be part of the return deal.
The offer was promptly rejected by the government.
Government peace commissioner Luis Carlos Restrepo last week offered to meet Farc delegates "any place, any time", but made clear no territory would be demilitarised.
"This government is not going to remove its security forces in order to meet with the Farc or anybody else," a government spokesman told Reuters.
General Carlos Alberto Ospina, commander of Colombia's armed forces, said Farc wanted the areas cleared in the western province of Valle del Cauca because it was "getting walloped and... wants the operations to stop".