She has been held captive in a South American jungle for nearly six years, becoming an international symbol of Colombia’s hostage crisis as uncertainty over her fate mounted.

Yesterday Ingrid Betancourt, 45, a former presidential candidate and bestselling author, was shown alive on a video seized from guerrillas by security forces.

In the video, which has no sound, a gaunt Ms Betancourt is shown sitting on a chair and staring blankly at the ground. Her hair has grown past her waist. Images of three US contractors seized by the Revolutionary Armed Forces of Colombia (Farc) rebels a year after her were also shown.

Her family were overjoyed at the first evidence in four years that Ms Betancourt was alive but they were deeply worried about her appearance. “We are extremely moved, very, very moved, to see these images of my sister,” Astrid Betancourt said on French television.

“So far we have only seen a single photograph. It looks like her hand is chained. It is a sad image of my sister, but she is alive.”

The hostage’s mother, a former Colombian beauty queen, was in tears. “I am in a lot of pain seeing her this way, so skinny and chained,” Yolanda Pulecio said on Colombian radio.

The last time she was seen in a video, in 2003, Ms Betancourt struck a defiant tone and called on the Army to rescue her. She also said that hostages should not be exchanged for prisoners, something that is being attempted these days.

Ms Betancourt, who is from a wealthy international background and who was once profiled in Vanity Fair, has long campaigned against drugs and corruption in Colombia. She holds French citizenship by virtue of her first marriage, to a French diplomat, and is something of a cause célèbre in France, where she has become a symbol of courage.

She topped the bestseller lists with her autobiography, Storm in My Heart, and some reviewers hailed her as a modern-day Joan of Arc. Her 2002 presidential election campaign was followed closely in France even before her kidnapping.

In 2003 it emerged that France had participated in a botched secret effort to rescue Ms Betancourt. The operation, which came into the open after Brazilian officials became suspicious about a French C130 troop carrier that landed mysteriously at Manaus airport, caused a storm in France.

It was alleged that Dominique de Villepin, the French Foreign Minister, had sent the secret service on a reckless and ill-conceived adventure to rescue Ms Betancourt, a former student of his and personal friend.

Brazilian officials suspected further that France had been preparing to pay a ransom for her release in the form of arms or money behind the backs of the Colombian and Brazilian authorities. The allegations were denied vehemently by the French Government.

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