Armed groups, criminals and others have carried out 66 massacres across Colombia this year, the UN said Tuesday, urging action to protect civilians against the violence that has been "normalised".

"It is tragic to see so many people fall victim to persistent violence across the country," UN human rights chief Michelle Bachelet said in a statement, noting that peasants, indigenous and Afro-Colombian people especially were targeted.

"In addition to those killed, the victims, of course, include those left behind, who remain almost completely defenceless," she said.

Her office has documented a total of 66 massacres across 18 of Colombia's 32 departments in 2020 alone, leaving 255 people dead.

It said it had also learned that 120 human rights defenders have been killed in the country this year. Since the signing of a peace agreement in the country in 2016, the UN has also documented 244 killings of former FARC fighters.

The Nasa community was one of the indigenous groups worst affected by the swelling violence in the country, with 66 of its members in northern Cauca reported killed in 2020, the UN said.

Most recently, five people including a former FARC fighter in the process of being reintegrated were reported killed in two separate incidents in northern Cauca on December 5. "On the same day, 24 leaders and authorities of the Nasa people received death threats," Tuesday's statement said.

It also pointed to an attack on December 3 in Choco department, where indigenous leader Miguel Tapi Rito was killed.

The attack spurred some 900 people in his community, most of them women and children, to flee to a nearby town, "where they have been begging the state authorities to provide them with protection."

"I call on the Colombian authorities to take stronger and much more effective action to protect the population from this appalling and pervasive violence," Bachelet said.

She stressed the need for the country to develop a public policy to dismantle "the criminal groups that succeeded paramilitary structures and their support networks," as was stipulated in the 2016 peace agreement.

She called on the Colombian authorities to conduct "prompt, thorough, impartial, independent and transparent investigations" into all allegations of rights abuses, and to ensure victims have access to justice and redress.

"Sadly, violence has been normalised in Colombia after decades of armed conflict, and no one should accept that," Bachelet said.