The offer comes as political violence by criminal groups threatens peace in the country. Gangs formed from right-wing paramiltary groups are blamed for much of the violence targeting rights activists.
Colombian President Juan Manuel Santos on Monday signed a law to induce criminal gangs to surrender in exchange for reduced sentences.
The South American country has witnessed a wave of political murders since the government signed a peace treaty with the left-wing rebel Revolutionary Armed Forces of Colombia (FARC) in 2016.
At least 311 rights activists have been killed from January 2016 to June 2017, threatening the long-term sustainability of a peace agreement that ended a half-decade civil war.
The attorney general's office said last week that guerillas from the ELN, dissident FARC rebels, and narcotrafficking gangs, especially the Gulf Clan, were responsible for the violence.
Criminal gangs formed from right-wing paramilitary groups have targeted human rights and land rights campaigners who challenge their economic and political interests. The gangs have also sought to control drug trafficking routes.
The measure signed by Santos would reduce prison sentences by 50 percent if whole groups collectively turn themselves in.
The powerful Gulf Clan has indicated that it may be willing to surrender.
Securing the peace in areas once controlled by FARC will be a major challenge for incoming conservative president Ivan Duque, who takes office in August.
cw/jm (AP, dpa, EFE, Reuters)