PARIS, France (CNN) -- French President Nicolas Sarkozy will send a humanitarian mission to Colombia's jungles to treat ailing hostages held by leftist rebels there, Colombian President Alvaro Uribe said Tuesday.
French President Nicolas Sarkozy urged Colombian rebels to release a hostage with dual French citizenship.
"Sarkozy has expressed to me that a humanitarian mission to attend to the health of the hostages is in movement," Uribe said.
Uribe said that Sarkozy asked him to guarantee safe passage of the mission, which will include the Red Cross, and that he promised to suspend military operations in the area to help the mission's work.
It was not immediately clear when the mission is to begin. Uribe did not offer additional details.
A spokesman at the Elysee Palace in Paris confirmed the mission.
Uribe's announcement came hours after Sarkozy appealed to the Revolutionary Armed Forces of Colombia, or FARC, to free former Colombian presidential candidate Ingrid Betancourt. Sarkozy said she is "in danger of imminent death."
Addressing Manuel Marulanda, a FARC leader, Sarkozy said in a televised national address that Betancourt "doesn't have the strength to withstand this endless captivity, which is turning into a tragedy."
FARC has held Betancourt, who has dual French citizenship, for more than six years. Hostages whom the rebel group recently freed said she is in poor health, and other reports have said she began a hunger strike February 23, the sixth anniversary of her captivity.
Sarkozy did not mention that claim.
He said his country stands ready should FARC decide to release her or other hostages.
"France awaits only one sign from your part to immediately organize, in concert with the competent authorities, a humanitarian mission to help take care of Ingrid and the weakest hostages," he said.
"So, you who lead FARC, you now have a date with history," Sarkozy warned. "Don't miss it. Liberate Ingrid Betancourt and those hostages who are the weakest!"
Not doing so, he said, "would be a severe political error, in addition to being a humanitarian tragedy. It would be a crime. You would be responsible for the death of a woman."
Sarkozy's remarks came as the Agencia Bolivariana de Prensa Noticias Web site published a letter from the rebel group that said Betancourt's chances of freedom have diminished in the wake of a Colombian attack on a FARC camp inside Ecuador.
The March 1 attack killed about two dozen people, including Raul Reyes, FARC's second-in-command, as well as an Ecuadoran and several Mexicans.
Ecuador broke off diplomatic relations with Colombia after the attack, criticizing it as an assault on its territorial sovereignty.
"There will not be a meeting with the French delegation over the release of Ingrid," Ivan Marquez, a FARC member, wrote in the March 20 letter published Tuesday on the ABP Noticias Web site.
"As commander Manuel said: 'They killed Raul, and seriously wounded the exchange of prisoners and peace,' " Marquez wrote in the letter.
The letter was apparently written before the Colombian government made an offer last week to free jailed guerillas if FARC freed hostages, including Betancourt.
The Colombian government said it was prepared to suspend the sentences of imprisoned FARC fighters if the rebel force freed high-profile hostages, such as Betancourt or three U.S. defense contractors held since 2003, the government's high commissioner for peace, Luis Carlos Restrepo, said in a written statement.
Established as the military wing of the Colombian Communist Party in 1964, FARC is Colombia's oldest, largest and best-equipped Marxist rebel group, according to the U.S. Department of State. Several nations, including the United States, classify it as a terrorist group.
FARC has long justified hostage-taking as a legitimate military tactic in a drawn-out, complex civil war that has involved right-wing paramilitary groups, government forces and drug trafficking.
The group holds roughly 750 hostages in Colombia's jungles.