By Patrick Markey

BOGOTA, Jan 15 (Reuters) - Letters sent by Colombian hostages from jungle camps revealed on Tuesday how they are chained up, weak from illness and desperate for leaders like Fidel Castro to help secure a deal with Marxist rebels to free them.

The notes and pictures from guerrilla hostages were brought by former congresswoman Consuelo Gonzalez who was released last week after nearly six years in rebel captivity in a deal brokered by Venezuela's left-wing President Hugo Chavez.

The release of Gonzalez and fellow captive, Clara Rojas, has raised hopes for an accord to free other hostages kept by Latin America's oldest insurgency, including French-Colombian politician Ingrid Betancourt and three Americans.

But letters from those left behind like Police Col. Luis Mendieta, captured nearly a decade ago, show their precarious health fighting off sickness after long jungle marches and frustration following years in insect-infested camps.

"It is not the physical pain that wounds us, nor the chains on our necks that torment us or the constant sickness ... it's the mental agony of the irrationality of all this," says one letter signed by Mendieta and others read on local radio.

"It seems that we are worthless, that we do not exist."

Details of suffering from recent hostage letters have shocked Colombians even as violence from their four-decade conflict eases under President Alvaro Uribe, a Washington ally who has led a campaign to drive the rebels into the jungles.

The Revolutionary Armed Forces of Colombia, known as the FARC, is still holding several hundred hostages for ransom or political leverage. Authorities said the rebels kidnapped six Colombian tourists on Sunday from a remote Pacific beach.

Mendieta wrote that he has been chained to a pole and spends days trying to pass time playing cards and learning English and Russian in rudimentary classes from another hostage.

Sickness has forced him to be carried several times in a hammock. Injections have eased ailments in his legs and feet, but at times he cannot walk.

"I had to drag myself to the bathroom for my necessities through the mud with just the strength of my arms because I could not get up," he wrote in a letter read by his daughter.

'PLEASE SAVE THIS LIFE'

Blurry photos show Mendieta with former local governor Alan Jara and ex-congressman Luis Eduardo Gechem and other police hostages, who have been held by the FARC for more than five years in secret camps.

In one letter read by Gechem's wife he appealed for help from Cuba, which has been host to attempts to broker a peace deal with Colombia's second largest rebel group the ELN. The FARC have also shown affinity for Cuba's revolution.

"President Fidel Castro, I ask you, beg you to make an additional gesture for humanity," Gechem wrote. "Comandante Castro please save this life."

After a failed attempt at the New Year, Chavez last week helped negotiate the release of Rojas and Gonzalez, who were held for nearly six years by the FARC, which Washington brands a drug-trafficking terrorist group.

Rojas gave birth to a child in captivity who was taken from her months after he was born. They were reunited at the weekend in Bogota.

Chavez, a foe of Washington, has stirred tensions with Colombia by demanding Uribe recognize the FARC's political status and has urged foreign governments to take the group off their lists of terrorist organizations.

Uribe says that can only happen when the FARC commit to a peace process.

The rebels, who began as a peasant army fighting for socialism in the 1960s, are insisting Uribe pull troops from an area roughly the size of New York City in southwest Colombia to facilitate any hostage deal.

But Uribe, a hardliner whose father was killed in a botched FARC kidnapping more than 20 years ago, refuses their conditions saying creating such a safe haven would allow the guerrillas to regroup. (Reporting by Patrick Markey in Bogota, editing by Jackie Frank)

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