Ingrid Betancourt is the highest-profile Farc hostage
A French plane and medical team are on standby in case the high-profile hostage Ingrid Betancourt, held by Colombia's Farc rebels, is released.
The French president's office said it was a "precautionary" move and that there was no information to suggest Ms Betancourt was about to be freed.
The former Colombian presidential candidate and dual French-Colombian national is believed to be gravely ill. She has spent more than six years as a hostage of the left-wing Farc group.
Last week, the Colombian government offered prisoner amnesties in exchange for hostages and said France could take freed Farc prisoners as part of a deal.
In a interview with the BBC, a spokeswoman for President Nicolas Sarkozy said a French army Falcon 900 business jet carrying medical equipment had arrived at an airport near French Guiana's capital, Cayenne, on Friday.
Aurelia Jublin said the jet had parked at the military base adjacent to the airport and been placed on stand-by to evacuate Ms Betancourt should she be released.
The plane will remain there until Monday, when it is due to be replaced indefinitely by a sophisticated aircraft equipped with high-tech medical equipment, which will be available to fly out at a moment's notice.
Ingrid Betancourt before her kidnap (left) and several years later (right)
Born on 25 December 1961
Grows up in Paris
1989: Returns to Colombia
1994: Elected to lower house
1998: Becomes a senator
2002: Kidnapped by Farc rebels
Ms Jublin stressed that the plane's mere presence in French Guiana should not be read as a sign that France has been involved in any kind of secret negotiations to secure Ms Betancourt's release.
The Colombian Interior Minister, Carlos Hoguin, welcomed the move, saying that the guerrillas who are holding Ms Betancourt "must understand that a humanitarian gesture is required".
Ms Betancourt, 46, is the most high-profile of the scores of hostages held in the jungle by Farc. She is said to have hepatitis B and a tropical skin disease and was pictured in a recent video, looking thin and frail.
Ms Betancourt was kidnapped in 2002 after she entered Farc territory for unofficial talks with the rebels while campaigning for the Colombian presidency.
Her case has drawn broad international attention for years and in particular in France, as she holds French nationality acquired through her marriage to a French national.
On Saturday, her former husband said he feared she might no longer be alive.
"I am afraid that Ingrid Betancourt is either dying or already dead," Fabrice Delloye told the AFP news agency.
Last week, Colombian President Alvaro Uribe announced the establishment of a $100m fund for any information leading to the whereabouts of the hostages.
The Farc has been involved in conflict in Colombia for decades
Mr Uribe urged Farc fighters to accept his offer of cash rewards and reduced jail terms for abandoning rebel ranks and releasing kidnap victims.
The Farc, which has been fighting the Colombian state for five decades, is yet to respond to the proposal.
Analysts say the promise of exile in France could be attractive to anybody wanting to turn themselves in, since the Farc has a policy of hunting down and killing deserters.
In addition, Ms Betancourt's release would be a coup for President Sarkozy, whose popularity has slumped at home.