BOGOTA - In dramatic detail, a letter from Colombian rebel hostage Ingrid Betancourt portrays how she struggles to survive and maintain hope after nearly six years in secret guerrilla camps.

Videos, letters and photographs of Betancourt, a Colombian-French politician, and other kidnap victims were confiscated from captured rebels and images of the gaunt hostages broadcast on Friday have shocked Colombians.

"Physically I am in bad shape. I don't eat anymore, my appetite is blocked, my hair falls out in clumps," Betancourt writes in an excerpt of a letter to her mother printed in El Tiempo newspaper on Saturday.

"I don't have enthusiasm for anything because the only answer for everything here in the jungle is No," she writes. "I no longer have the same strength, now it is struggle for me to keep believing."

The documents were the first evidence since 2003 that Betancourt could still be alive.

A former presidential candidate snatched in 2002, Betancourt is one of the highest-profile hostages held by the Revolutionary Armed Forces of Colombia, known as the FARC, who have also kept three Americans captive since 2003.

Though weakened by President Alvaro Uribe's U.S.-backed security crackdown, the FARC are still fighting Latin America's oldest insurgency, fuelled by the cocaine trade. The rebels hold scores of hostages for political leverage and ransom.

Attempts by Venezuelan President Hugo Chavez to broker a deal to free hostages fell apart last week when Uribe cancelled the left-wing leader's mediation efforts, charging he broke with protocol and sparking a diplomatic spat.

Images from the captured videos show Betancourt very thin sitting silently in a jungle clearing. Others show the three Americans: Keith Stansell, Marc Gonsalves and Thomas Howes. Howes sends a message to his family and a copy of his will.

Betancourt tells how she lives in a hammock with her belongings packed ready to march. She says she has tried to escape and many of her belongings have been confiscated by her rebel captors. Her only luxury is a Bible, she says.

"For three years, I have been asking for an encyclopaedia to read something, to learn something, to keep alive my intellectual curiosity," she writes.

Betancourt says she is the only woman in a group of eight to 10 captives. She sends messages to her children, husband and sister, asking her daughter living in Paris to promise to study for a doctorate.

Negotiations over a hostage deal have been stymied by rebel demands for a demilitarized zone, which the government refuses. But Uribe has said he is willing to work with French President Nicolas Sarkozy to broker a possible hostage deal.

"My heart belongs also to France," Betancourt writes. "When the night is at its darkest, France is a lighthouse."