France abandoned a mission to treat Colombian rebel hostage Ingrid Betancourt in her jungle camp on Tuesday after guerrillas rejected the initiative in a setback to attempts to free scores of captives.

The rejection was a disappointing blow to French President Nicolas Sarkozy, who has made it a priority to secure the freedom of the dual French-Colombian citizen kidnapped by the Revolutionary Armed Forces of Colombia, or FARC, while campaigning for the presidency in 2002.

Sarkozy said in a statement he was "deeply disappointed" and his foreign minister would travel to the region soon. Paris said the medical mission, backed by Spain and Switzerland, would leave Colombia shortly.

"France will stay fully mobilized to ensure the hostages return to life and to their families," Sarkozy said.

Betancourt, three Americans and dozens of politicians, police and soldiers are among 40 political captives whom the FARC says it wants to exchange for jailed fighters. But the guerrillas and government are deadlocked over a hostage deal.

The French medical mission flew into a Bogota air base on Thursday to treat Betancourt, who is believed to be sick after more than six years in captivity. But the mission was in doubt from the start as Paris had no prior deal with the rebels.

"The French medical mission is not reasonable and even less so when it was not the result of any agreement," the FARC said in a statement dated April 4 and posted on a Web site that often carries rebel communiques.

"We do not respond based on trickery or media campaigns," the rebel statement said.

Colombia's four-decade-old conflict has eased under President Alvaro Uribe, a Washington ally who has used billions of dollars in U.S. aid to fight Latin America's oldest surviving insurgency and the cocaine trade.

In their statement, the rebels stood by their demand that Uribe demilitarize a New York City-sized area around two rural towns, Florida and Pradera, to facilitate a prisoner swap.

Uribe, a conservative who is popular for driving back the rebels, has rejected the condition because he says it would allow the FARC to regroup. He has offered a smaller zone under international observation for any handover.

SECOND FRENCH MISSION

A flurry of rumours over the last few weeks fuelled concern over Betancourt's health. Reports surfaced the FARC had taken her to be treated in rural clinics in jungle areas, where they are still a potent force. But there was no solid confirmation.

Hostages released this year say she is seriously ill and has been chained up after attempting to escape. A rebel video broadcast at the end of last year showed the former lawmaker pale and gaunt in the jungle.

"This is like a bucket of cold water tossed over us, it's very sad," Betancourt's husband Juan Carlos Lecompte told Reuters television in Bogota. "But it was expected in any case and I still have hope as hope is the last thing you lose."

France tried a similar mission in 2003, flying a military transport plane to Brazil's border with Colombia after Betancourt's family heard she could be freed. But the initiative failed with Colombia and Brazil criticizing Paris.

"This rejection contributes to the contamination of the atmosphere," said Alfredo Rangel at Bogota's Security and Democracy Foundation think tank. "It shows the need again to find intermediaries who enjoy the trust of both sides."

The International Committee of the Red Cross, whose neutrality helped in the release of six hostages this year in a deal brokered by Venezuelan President Hugo Chavez, was never contacted by rebel sources on the French initiative.

Chavez's role in hostage negotiations fuelled tensions with Bogota, which was angered by his open support for more political recognition for the FARC. The rebels have also resisted attempts by the Roman Catholic Church on talks.

Originally a peasant army fighting inequalities in the 1960s, the FARC is now funded by extortion and cocaine trafficking. Rebels have little popular support and U.S. and European officials label them a terrorist organization.