(Updates with sister's comments, doubts over mission) By Patrick Markey BOGOTA, April 4 (Reuters) - A French medical mission to treat ailing Colombian rebel hostage Ingrid Betancourt remained grounded at a Bogota air base on Friday, dogged by doubts after a tough guerrilla rejection of calls for her swift release. Betancourt, a French-Colombian citizen and former presidential candidate kidnapped in 2002, is the highest profile hostage being held by the Revolutionary Armed Forces of Colombia, or FARC. A French aircraft carrying a medical team arrived on Thursday and sat on the tarmac at Catam military base waiting to fly into the jungles, where former hostages say Betancourt is very sick with hepatitis and other illnesses. French Foreign Minister Bernard Kouchner on Friday acknowledged that France was waiting for a response from rebels about the mission to aid Betancourt, and her sister was unsure the team would reach her without a prior deal with the FARC. "Are we pessimistic about a result from this French mission? Yes," Astrid Betancourt told local radio. "If this is a success in any way, it will be a miracle as there was no prior agreement." A top FARC commander said on Thursday that Betancourt would not be handed over immediately. He said the group's captives, who include three U.S. contractors and dozens of politicians, police and soldiers, could only be freed through a negotiated agreement to swap hostages for jailed rebels. But he gave no direct signal whether the medical team would be allowed into the jungle camps. A French diplomatic source downplayed the FARC document, saying it had been dated before the mission was planned. The International Committee of the Red Cross, which has helped in previous hostage initiatives, says it has had no contact with rebels over the medical mission and so far is not engaged in the French effort. 'WE'RE TRYING, TRYING' Kouchner said France kept working for the mission and told reporters that President Nicolas Sarkozy, who has made Betancourt's release a priority, would travel to meet Venezuelan President Hugo Chavez if it helped free her. "We're trying, trying, trying and there's no other solution," he told Europe 1 Radio. Chavez, a left-wing foe of Washington, has helped broker the release of six FARC hostages this year. His involvement and demands for political recognition for the Marxist rebels have fueled tensions with neighboring Colombia, a White House ally. Captives freed recently have described Betancourt as being in very poor health and say she has been chained up after several escape attempts. A rebel video shown last year showed her gaunt and despondent in a jungle camp. Violence from Colombia's war has eased as President Alvaro Uribe's U.S.-backed troops push rebels into remote areas. The FARC is still fighting and has an estimated 9,0000 guerrillas but is labeled a cocaine-trafficking terrorist group by U.S. and European Union officials. Betancourt and her vice presidential running mate Clara Rojas were captured at a rebel roadblock during the presidential election campaign in 2002. Rojas was one of the six hostages recently freed. The FARC says it wants to swap 40 key hostages, including Betancourt and the three Americans captured in 2003, for jailed rebels. Attempts to reach a deal are deadlocked over a FARC demand that Uribe pull back troops from a swath of land. The death of two top FARC commanders in Colombian military raids in March also has complicated talks. One commander, Raul Reyes, was a FARC spokesman and a key French contact in negotiating a hostage accord. (Additional reporting by James MacKenzie in Paris; Editing by Bill Trott and Kieran Murray)
Oscar Tulio Lizcano (C), Colombian politician kidnapped since August 2000 by The Revolutionary Armed Forces of Colombia (FARC), is seen in a video showed by congresswoman Piedad Cordoba in Bogota April ...
