French President Nicolas Sarkozy has made a direct appeal to Colombian rebels to release Ingrid Betancourt, a long-held French-Colombian hostage.
Ms Betancourt says she has been "living like the dead"
"I have a dream: to see Ingrid among her family this Christmas," Mr Sarkozy said in the televised message.
Last week, Ms Betancourt was shown looking thin and haggard in a video seized by Colombian authorities.
After seeing it, Mr Sarkozy vowed to redouble his efforts to free her after a regional mediation effort failed.
Ms Betancourt - who has French nationality through a former marriage - was kidnapped in 2002 while campaigning for the Colombian presidency.
She was one of 45 high-profile hostages whose freedom Venezuelan President Hugo Chavez tried to secure in exchange for about 500 imprisoned guerrillas from the Revolutionary Armed Forces of Colombia (Farc).
The exchange bid was strongly supported by relatives of rebel hostages, but collapsed after the Colombian president accused Mr Chavez of breaking an agreement.
'Danger of death'
The collapse of the mediation attempt was lamented at the time by Mr Sarkozy, and early on Thursday he made a direct appeal to Farc chief Manuel Marulanda to free Ms Betancourt.
"I do not share your ideas and I condemn your methods," Mr Sarkozy said in the message broadcast on French television, reported AP news agency.
"I ask you solemnly to release Ingrid Betancourt and not carry on your conscience the risk that her departure would bring," he said.
"You must save a woman in danger of death. You can show the world that the Farc understands humanitarian imperatives. Monsieur Marulanda, you carry a great responsibility."
Of Ms Betancourt, he said: "The flame is going out from this woman whose energy, audacity, courage, forced admiration from all who knew her."
In the video and photos released last week, Ms Betancourt was shown in a jungle setting, looking gaunt and subdued, along with 15 other hostages.
The following day, a letter was released from Ms Betancourt to her mother, in which she said her strength had diminished, her appetite had gone, and her hair was falling out.
"Here, we are living like the dead," she wrote.