The French mission to treat an ill French-Colombian hostage held by the Revolutionary Forces of Colombia (FARC) appears to be unsuccessful, as the rebels who have been battling Colombian forces for more than 40 years declared they would only release hostages in exchange for jailed rebels.

An aircraft transporting the French medical team landed Thursday morning at a military air base in Bogota, the country’s capital, after the son of hostage Ingrid Betancourt, said in a news conference in Paris that his mother was very ill and needed a blood transfusion within hours, in order to stay alive.

Rodrigo Granda, the main leader of the rebel group, who was released last year by Colombian President Alvaro Uribe in exchange for hostages, said FARC had no deal with France to release Betancourt and that the only way to free hostages is to release from jail around 500 guerillas.

"Only as a result of a prisoner exchange will those who are held captive in our camps go free," Granda said in a communique posted Thursday on the website used by FARC.

French president Nicolas Sarkozy asked Uribe to help France by guaranteeing safe passage of the humanitarian mission, but he did not wait for the FARC leaders to confirm they agreed to release Betancourt or at least allow the medical team to treat her.

“If there was no agreement, this (mission) could be delayed for a long time waiting for the FARC to say yes, or it probably won't happen at all,” Carlos Lozano, director of Voz, the communist party newspaper, told the Associated Press in a telephone interview.

The rebel group insisted that, for any hostage release, they requested the freedom of two FARC leaders held in prison in the United States: Nayibe "Sonia" Rojas and Simon Trinidad.

Ingrid Betancourt was captured by rebels in 2002, while she was campaigning for the presidency. After several attempts to escape, she was chained to a tree, revealed the hostages that were recently released by FARC.