The French Foreign Minister Bernard Kouchner has said he is "not very optimistic" about freeing the hostage, Ingrid Betancourt.

Ms Betancourt, who is French-Colombian, has been held for more than six years by the rebel Farc group in Colombia, and is in very poor health.

Mr Kouchner said that, nevertheless, his recent trip to Latin America had been "very useful".

The French government has made securing Ms Betancourt's release a priority.

Mr Kouchner told a radio station that his visit to Colombia, Venezuela and Ecuador had helped to re-establish contact with leaders including Venezuela's President Hugo Chavez, who has been influential in securing hostage releases from Farc in the past.

The French foreign minister believes that President Chavez could play an important role in negotiations.

Ms Betancourt is Farc's highest-profile political hostage.

She is believed to suffer from serious liver problems and was pictured looking frail in a recent video.

France sent a mission to Colombia last month in the hope of providing medical treatment for Ms Betancourt.

Farc has freed six hostages this year and wants to exchange others for hundreds of rebels currently in prison, including three jailed in the United States.

Negotiations have stalled since the killing of France's main rebel contact, Raul Reyes, in a Colombian military raid into Ecuador on 1 March.

Farc - the Revolutionary Armed Forces of Colombia - has been fighting to overthrow the Colombian government for more than 40 years.