The main leftist rebel group in Colombia, FARC, has said it is not holding eight foreign tourists kidnapped in the jungle last week.
FARC has kidnapped thousands of people
FARC had been blamed for snatching the four Israelis, two Britons, a German and a Spaniard who have not been seen since they were abducted on Friday.
The BBC's Jeremy McDermott in Colombia says the focus of suspicions will now fall on another rebel group, the National Liberation Army, as well as right-wing paramilitaries and drugs traffickers who operate in the Sierra Nevada region where the group was snatched.
Most of Colombia's 3,000-odd kidnappings every year are carried out by FARC, who use the ransoms to fund their 39-year war on the state.
Thousands of troops have been searching for the tourists.
In a separate development, Colombian President Alvaro Uribe and his Brazilian counterpart, Luis Inacio Lula da Silva, met on Tuesday to discuss the possibility of a meeting between United Nations officials and FARC aimed at advancing a peace process.
The Brazilian Government, which does not officially classify FARC as a terrorist organisation, has offered to host such a meeting.
Earlier, an Australian tourist spoke of how he escaped from the group being held captive.
Mark Tuite and his wife were among five foreign tourists left behind when the rebels raided their camp during a trekking trip to ancient ruins.
Mr Tuite, 33, believes he may have been spared because his footwear was ill-suited to a fast jungle march and because he and his wife would have defended each other.
Israelis: Beni Daniel, 26,
Orpaz Ohayon, 22, Ido Yosef Guy, 26, and Erez Altawil, 24
Britons: Mark Henderson, 31, and Mathew Scott, 19
Spaniard: Asier Huegun Echeverria, 29
German: Reinhel Welgel
He and his wife Michelle said the group was woken early on Friday morning by heavily armed men in uniform telling them they were being moved to a safe place because there had been a shooting in the area.
"We packed our bags and they started going on about how we were only wearing sandals," he said.
"They kept saying: 'You have to put good shoes on because we're going a short but quick march'.
"We said 'no', and that we trekked up here in these sandals and they're the only shoes we've got."
Another tourist told him that the men had tied up their guides.
Mr Tuite said two couples and another tourist were then separated from the group and had their hands and legs bound and locked in a room.
"From what we've been led to believe, they don't like to hassle with couples, because they'll stick up for each other and create more hassles than a person by themselves, and that's it.
"They were polite but firm, if you know what I mean. They seemed like a very professional, well-oiled machine.
"When we got back into the hut and they tied us up, they took my sandals off and they did it better than a shoe store attendant would have."