PARIS, April 1, 2008 (AFP) - French President Nicolas Sarkozy pleaded Tuesday with Colombia's FARC rebels to release former Colombian presidential candidate Ingrid Betancourt who he said was so sick she might die.

'Ingrid is in danger of imminent death,' he said in a televised appeal to FARC leader Manuel Marulanda, the latest in a series of French initiatives to secure the release of the joint Colombian-French national.

'She no longer has the strength to resist an interminable captivity that is turning into tragedy,' said Sarkozy, who met earlier Tuesday with the head of a support committee to free Betancourt.

'Therefore, you who lead the FARC, you now have a rendezvous with history. Do not miss it. Free Ingrid Betancourt and those of the other hostages who are weakest,' he added.

Betancourt, who is thought to be gravely ill after six years in captivity in the Colombian jungle, has become a cause celebre in France due to high-profile campaigning by her family and friends here.

The 46-year-old is believed to be suffering from hepatitis B and leishmania, a skin disease caused by insect bites. Videos seized from the rebels in November showed her looking gaunt and frail.

France last weekend put a plane and a medical team on standby in case she is freed.

Betancourt was captured in February 2002 by guerrillas of the Revolutionary Armed Forces of Colombia (FARC) while campaigning for the Colombian presidency.

The Marxist FARC, which has been fighting the Colombian government for more than 40 years, is believed to be holding more than 700 people hostage in the jungles of the Latin American state.

Betancourt is among 39 high-profile hostages, including three US defence contractors, whom the FARC wants to exchange for 500 rebels held in prison.

The president of a Betancourt support group in France said Tuesday that she had been on hunger strike since February 23 and called for urgent action to secure her release.

Prime Minister Francois Fillon repeated Tuesday that France was ready to offer political asylum to FARC rebels freed from prison in exchange for Betancourt.

The International Federation of Human Rights (FIDH) and support groups for Betancourt meanwhile issued a joint appeal to Colombia to stop all military operations against rebels.

President Alvaro Uribe must 'order an immediate end to all the military operations that threaten the lives of people held hostage by the FARC,' wrote the FIDH and the support groups in an open letter to Uribe.

'It is with immense concern that we have noted that military operations and bombing continue and are intensifying in the regions where it is presumed that the FARC hold people in captivity,' they wrote.

The letter said that if Betancourt or others died because of Colombian army attacks, 'you (President Uribe) will no longer be the democratic leader you aspire to be but the torturer of these defenceless people.'