One of the hostages, 19-year-old Briton Matthew Scott, escaped soon after being taken from the Lost City ruins on 12 September.

The seven remaining hostages - four Israelis, a Briton, a German and a Spaniard - are thought to be in the Sierra Nevada mountains.

Colombian President Alvaro Uribe - who is travelling to the US to meet UN Secretary General Kofi Annan - has appealed to the rebels to release them.

"We want to express our willingness to find a solution to this operation," the National Liberation Army (ELN) said in the statement sent to a local radio station.

Manhunt anger

The Cuban-inspired ELN condemned the military operation to hunt for the kidnapped tourists.

It warned that Mr Uribe would be to blame if the hostages came to any harm.

"In the case of lamentable acts that could occur because of the presence, or the actions, of the army and paramilitary groups in the area, President Uribe would be held personally responsible," the rebels said in their statement.

HOSTAGES HELD Briton: Mark Henderson German: Reinhilt Weigel Israelis: Beni Daniel, Ortaz Ohayon, Ido Joseph Guy, Erez Altawil Spaniard: Asier Huegun

Mr Uribe accused the ELN of the abductions last Friday and demanded the group set the backpackers free.

The Colombian president is scheduled to speak to Kofi Annan about a meeting between the UN and Colombia's largest rebel group, the FARC, the Revolutionary Armed Forces of Colombia.

Mr Uribe has refused to negotiate with the guerrillas until they call a unilateral ceasefire - something the rebels have rejected.

But they have agreed to meet with the UN and Brazil has offered its territory as a venue for talks.

Last week 55 US congressmen signed a letter expressing profound concern over the Colombian president's plan to make peace with the brutal right-wing paramilitaries, responsible for some of the worst atrocities in 39 years of civil conflict.

Church mediators

The ELN said the hostages were taken in an operation called "Allende Lives" - timed to mark the 30th anniversary of the Chilean coup that overthrew Marxist President Salvador Allende and brought General Augusto Pinochet to power.

On Saturday, the Catholic Church in Colombia offered to mediate with the rebels as security forces intensified their efforts to rescue the remaining hostages.