BOGOTA : Colombian President Alvaro Uribe on Friday pressured FARC rebels to free hostages including the Franco-Colombian Ingrid Betancourt after his government offered what amounted to a prisoner swap.

"I am today calling on those holding doctor Ingrid Betancourt and the other hostages to liberate them, to make a big contribution to the country, to hear this cry from the heart of the Colombians," Uribe said in an address to the nation.

He promised an amnesty and payment from a 100-million-dollar state fund to those who obeyed and renounced their membership of the Revolutionary Armed Forces of Colombia (FARC), which Bogota has been fighting for four decades.

His words came one day after one of his senior officials, Colombian Peace Commissioner Luis Carlos Restrepo, offered to release FARC rebels from prison if their leftwing group freed Betancourt, 46.

The developments also followed accounts from ex-hostages and others that Betancourt -- who was snatched in February 2002 as she campaigned to become president -- was gravely ill.

Colombia's independent public ombudsman, Volmar Perez, said Thursday that Betancourt's captors took her to medical facilities in southeastern Colombia late last month.

"The information that we have, at least until February, is that the state of her health is very delicate, and her physical and health conditions have been deteriorating," he said.

He said that, according to residents in the area Betancourt was said to have been treated, the high-profile hostage was suffering from hepatitis B and leishmania, a skin disease caused by insect bites.

A Catholic priest in the region, Manuel Mancera, said Friday he had seen at least 200 rebels escorting Betancourt to the clinic of El Capricho near the town of San Jose de Guaviare.

Restrepo stressed those reports were uncorroborated but said Uribe "remains concerned" for Betancourt's health.

He also said the government was now willing to consider one of the rebels' key demands that its members be released from prison in return for the liberation of Betancourt and other hostages.

"It's enough that Ingrid Betancourt be immediately released for us to consider the humanitarian deal is on, enabling us to conditionally suspend the sentences of members of the rebel group," Restrepo said.

He did not say how many FARC rebels might be included in the swap, but said the government had "reduced to a minimum" its conditions for the exchange to happen.

Neither Uribe nor Restrepo spoke about the rebels' other key demand that a demilitarized zone be set up to facilitate negotiations, however.

That prompted Betancourt's husband, Juan Carlos Lecompte, to tell AFP the government's offer was unclear and he would have preferred "responses to the concrete demands of the rebels."

France, though, seized on the development, with foreign ministry deputy spokesman Frederic Desagneaux saying: "We call on the FARC to seize without delay this opportunity at a crucial moment."

He added that Betancourt "must urgently be freed."

Betancourt is the most prominent of the estimated 700 hostages being held by the FARC.

The rebel group has been holding out the prospect of freeing her and 38 others, including three US defense contractors, in exchange for 500 of its members rebels held in prison, including two held in US facilities.

Direct talks to negotiate the prisoner swap have never gotten off the ground, although the rebels unilaterally released six hostages to Venezuelan President Hugo Chavez earlier this year.

- AFP /ls