The hostages -- including three police officers and a soldier -- were kidnapped as they were traveling in a boat on the Arquia river in the Choco department.

The kidnapping took place just two days after outgoing President Juan Manuel Santos admitted defeat in his bid to sign a ceasefire with the National Liberation Army rebels ahead of his handing over power to hardline right-wing successor Ivan Duque on Tuesday.

The ELN, which confirmed it was responsible for the kidnapping, said Saturday that it informed the Colombian government peace negotiator that they were willing to free their hostages.

In a statement, the guerrillas urged the High Commissioner for Peace to get the Colombian military to create the "optimum security conditions" to facilitate the release.

The ELN "war front" that claimed the kidnapping said that in the Choco region there are intense military and paramilitary operations "that put at risk" the guerrillas and their hostages.

The statement added that the hostages were receiving proper protection and treatment.

The army earlier said the soldier who was kidnapped was on the boat suffering from a tropical disease, and was in was need of "urgent treatment."

President-elect Duque has called for a tougher stance on negotiations with the ELN, the last militant group fighting authorities in Colombia following the historic 2016 peace agreement signed with larger FARC guerrillas.