The guerrillas of the ELN or National Liberation Army said they would free Asier Huegun Etxeberria, from the Basque region, as a gesture of solidarity with the Basque struggle.

But they insisted Basque politicians must come to witness the handover.

Still being held are Briton Mark Henderson, four Israelis and a German.

The tourists were kidnapped last month while hiking in the Sierra Nevada mountains in northern Colombia.

Another Briton seized at the time managed to escape and make his way to safety.

Guerrilla links

Details of the release offer came from ELN spokesman Francisco Galan, who issued a statement from the Itagui high-security prison near Medellin, where he is serving a jail sentence.

Galan said the Basque people, like the Colombian people, had been victims of abuse and exclusion.

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

As a result, he said, the ELN had decided to free the Basque citizen Asier Huegun Etxeberria as a gesture of solidarity towards people fighting for sovereignty and independence.

But the ELN also said Galan should be freed to co-ordinate the handover and be given a radio-telephone - conditions that were rejected as unacceptable by President Alvaro Uribe.

The ELN are believed to have had contacts with the Basque separatist group, ETA, for many years.

The ELN say they are holding the remaining six tourists as political hostages, but no demands for political concessions that might secure their release have yet been made.