A senior leader of Colombia's Farc rebel group has ruled out any release of hostage Ingrid Betancourt until the government releases imprisoned rebel fighters, reports say.
Rodrigo Granda, the rebels' foreign relations chief, said those held would only be freed "only as a result of a prisoner exchange", a statement on an affiliated website said.
On Thursday a French aeroplane arrived in the Colombian capital as part of a medical mission to aid Betancourt, who is believed to be gravely ill after six years in captivity.
Betancourt, a former Colombian presidential candidate, may die if she does not get a blood transfusion, her son says.
Granda's statement did not explicitly rule out the possibility for the French medical doctors on the aeroplane to treat Betancourt, a French-Colombian national, in captivity.
Alvaro Uribe, the Colombian president, has vowed to make "all possible efforts'' in the mission to help obtain Betancourt's possible release.
His armed forces chief, General Freddy Padilla, also said that the military is prepared to assist the French mission, which includes two doctors and two diplomats, AP reported.
"The first objective of this mission is to succeed in getting close to Ingrid and care for her, then we hope the emissaries will be able to speak with the Farc and consider pulling Ingrid out of the jungle"
Betancourt's ex-husband, Fabrice Delloye
Speaking to France's BFM-TV on Thursday, Betancourt's ex-husband, Fabrice Delloye, said: "The first objective of this mission is to succeed in getting close to Ingrid and care for her.
"Then we hope the emissaries will be able to speak with the Farc and consider pulling Ingrid out of the jungle."
Pascale Andreani, a French foreign ministry spokeswoman, declined to provide details about the mission at a news briefing on Thursday.
She said: "Discretion is required in this type of case.''
The office of Nicolas Sarkozy, France's president, had said on Wednesday that a joint mission by France, Switzerland and Spain aimed at giving medical aid to Betancourt was on its way to Colombia.
Luis Carlos Restrepo, Colombia's peace commissioner, said the Colombian government was complying with a request by France that it suspend all military operations against the Revolutionary Armed Forces of Colombia (Farc) while the operation took place.
The mission follows weeks of concern over the former Colombian presidential candidate's health, in particular following news from hostages released earlier in the year who said Betancourt's health was failing.
Speaking at a news conference in Paris on Wednesday, Lorenzo Delloye-Betancourt, Betancourt's son, said these were the final hours of his mother's life unless drastic measures were taken.
"My mother is dying. She has Hepatitis B and leishmaniasis [a skin disease] which requires a blood transfusion in the hours to come or risks losing her life," he said.
Attempts to secure a deal to free the hostages, who also include three Americans, are deadlocked over a rebel demand that Uribe demilitarise an area in the south of Colombia for a safe haven to facilitate talks.
The Farc did release six captives earlier this year in a deal brokered by Hugo Chavez, Venezuela's president.
The Farc have been fighting a bitter four-decade civil war against the Colombian government, accusing it of oppressing the country's poor.
The government in turn accuses the group of extortion and profiting from drug-trafficking.
Thousands have been killed in the fighting.