The two groups have fought for control of smuggling routes near the border between Colombia and Ecuador.
At least 18 people were killed in Colombia in clashes between holdouts from the former rebel group FARC and another armed group linked to drug trafficking, the government has said.
The government ombudsman's office said on Sunday that the fighting occurred a day earlier in southwest Colombia, near the border with Ecuador.
The clashes involved rebels who have rejected a 2016 peace agreement that Revolutionary Armed Forces of Colombia (FARC) signed with the government and a criminal band that calls itself Comandos de la Frontera, or Border Commandos.
The latter is composed of other fighters that used to be with FARC and remnants of a right-wing paramilitary group active in trafficking cocaine to Ecuador and Brazil.
The two groups have fought for control of smuggling routes in parts of the Putumayo border area for at least three years.
The fighting occurred in Puerto Guzman, about 60 kilometres (37 miles) from the southern border with Ecuador, the government's ombudsman's office said.
READ MORE: Colombia kills top commander in 'blow' to FARC rebels
Resumption of peace talks
Colombia has been consumed by more than half a century of armed conflict between the state and various groups of left-wing guerrillas, right-wing paramilitaries and drug traffickers.
President Gustavo Petro's government is scheduled to resume peace talks on Monday in Caracas with the National Liberation Army (ELN), Colombia's last active rebel group, after a four-year hiatus.
Petro's administration and the much smaller renegade faction of the FARC involved in Saturday's fighting, known as the Carolina Ramirez Front, have held exploratory peace talks aimed at a truce.
Under those talks, the faction said it would rein in attacks on security forces, with an eye on a bilateral ceasefire.
READ MORE: Clashes between Colombia rebels kill over two dozen
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