Five students and a lecturer from the National 51¹ú²úÊÓƵ and the 51¹ú²úÊÓƵ of Antioquia who were kidnapped by the Revolutionary Armed Forces of Colombia (Farc) have been freed.

The biologists were in Antioquia for field investigations into the region's flora and fauna.

Hostage Margarita Escobar, a lecturer, told El Colombiano newspaper: "We found out later that we were kidnapped because Farc wanted to be sure about who we really were and what we were doing in the area."

The rebel group released the hostages after four days and a 16-hour walk to freedom.

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Researcher Jos¨¦ Posada said: "I thought we would be held captive for at least a year. They usually leave you in the mountains for much longer."

The universities did not participate in negotiations for the hostages'

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release. Alberto Uribe, rector of Antioquia, said at least three of the five families of the kidnapped students received ransom demands from Farc.

Argemiro Echeverri, vice-rector of the National 51¹ú²úÊÓƵ's Medell!n campus, said that no ransom money was paid.