The operation, which killed seven men and three women, was carried out in the municipality of Forful, in the South American country's department of Arauca, the army statement said.
It said the group had combined with local leaders of the National Liberation Army, or ELN by its Spanish acronym, to try to control drug trafficking in the departments of Arauca, Boyaca and Casanare, as well as coordinate "extortion activities, arms trafficking and the articulation of terrorist plans."
The ELN is currently in peace talks with Santos' government.
Santos signed a 2016 peace agreement with the Revolutionary Armed Forces of Colombia (FARC), the country's largest rebel group, which has since transformed into a political party.
But around 1,200 dissident combatants refused to lay down their arms and continue to operate in various parts of Colombia.
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