A former Colombian presidential candidate and three Americans who were kidnapped by rebels up to six years ago have been shown alive in a series of videos that have given renewed hope to their families.

Ingrid Betancourt, taken by rebels from the left-wing Revolutionary Armed Forces of Colombia (Farc) group while running for president in 2002, appeared chained, downcast and sickly in one of five films seized by Colombian troops, dated October 24.

Painfully gaunt with hair past her waist, she sits silent and motionless on a chair with her hands crossed over her legs, staring blankly at the ground.

Three US State Department contractors, Mark Goncalves, Keith Stanstell and Thomas Howes, seized in February 2003, feature in another video, dated January 1, 2007. Filmed, like Ms Betancourt, against a backdrop of thick jungle, they seem in better health and spirits than the politician.

Though the videos have no sound, Luis Carlos Restrepo, the Colombian government peace commissioner, said that the Americans were sending messages to their families. They were last seen in a 2003 film made by a Colombian journalist, while Ms Betancourt last appeared in a video shot by her captors on May 5, 2003, and broadcast on television three months ago.

Pictures of the hostages and letters written by them were also seized in the operation. Mr Restrepo said that one, dated October 24, was written by Ms Betancourt to her mother, Yolanda Pulecio, while in another, dated November 26, 2006, Mr Howes instructs changes to his will.

Ms Betancourt’s family spoke of their intense relief at seeing proof that the politician, who has French nationality from her first marriage, remains alive.

“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. She is sitting at a little table. She seems quite thin with very long hair. She’s looking down, sad. It looks like her hand is chained.

“It is a sad image of my sister, but she is alive,” she said.

The Americans and Ms Betancourt are among 45 hostages who the rebels want to exchange for 500 Farc prisoners. But talks have run aground on guerrilla demands for a demilitarised zone, rejected by President Alvaro Uribe.

Prospects for a swap dimmed further last week after the Colmbian President, Álvaro Uribe, ended a mediation effort by President Hugo Chávez of Venezuela, after he ignored Mr Uribe’s demand that he not contact his generals.

Ms Betancourt, who has become the international symbol of Colombia’s hostage crisis, was seized, along with her running mate Clara Rojas, by the leftist rebels as the pair drove to the southern town of San Vicente del Caguan. Ms Rojas has not been seen but Farc says that she is alive and has had a son, Emmanuel, in captivity, claims supported by a fellow hostage who escaped in May.

The Americans were kidnapped after rebels shot down their aircraft during an anti-drug surveillance mission.

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