In a video posted on YouTube, Ivan Marquez, the Marxist group's chief negotiator for the 2016 peace agreement, announced the birth of a group that he said would work "clandestinely."

"The members of the new movement will have a mission in the social sector where they live, work, or study, without it being public knowledge of their political affiliation," he said.

Marquez's whereabouts have been unknown for more than a year, but authorities suspect he has found refuge in neighboring Venezuela.

In the video, Marquez is dressed in a military uniform, with FARC flags hanging behind him. He is flanked by 15 armed men, including former rebel leaders Hernan Dario Velasquez, alias "El Paisa," and Jesus Santrich.

Santrich has been a fugitive since earlier this year after the United States sought to have him extradited on drug charges.

Last Thursday, the three rebel leaders announced a return to arms in another video message, accusing the Colombian government of betraying the peace accord signed with former president Juan Manuel Santos.

Under the accord, most of the FARC's 7,000 fighters disarmed after half a century of conflict and returned to civilian life after the accord. However, around 2,300 have refused to do so.

With Marquez at the helm, the rebels announced the creation of a new guerilla group, also called the FARC, which was initially transformed into a political party of the same name after the accord was signed.

After Marquez's original announcement, Colombian president Ivan Duque said Colombia was not "facing a new guerrilla, but facing the criminal threats of a gang of narco-terrorists."

He also accused Venezuelan president Nicolas Maduro of providing the group with "shelter and support."