During an event in Pasto city in the southwestern Andean region on Saturday, Comuneros del Sur said the delivery of explosives, grenades and other devices was a sign of the group's desire for peace.
"We consider that the armed fight is obsolete, that there are new times and new needs. We refuse to return to war," said Royer Garzon, one of the leaders of the armed group.
The move paves the way for eventual disarmament and reincorporation of some 300 Comuneros del Sur fighters into civilian life.
The deal is the most significant step toward peace since Petro assumed the presidency in 2022 with plans to end Colombia's internal conflict.
The group of about 250 fighters operates in Colombia's Southwestern Nariño province and has been in negotiations with the government since last year.
"This is a historic moment," Defense Minister Pedro Sanchez said in a ceremony in the town of Pasto, where several accords with the group were outlined by officials.
Sanchez said that over the past two days, the Commoners of the South have handed over land mines, grenades and rockets to an army unit that is destroying them.
"Farmers will be able to walk without the fear of coming across a minefield," Sanchez said.
Analysts said Petro's other peace efforts - with the National Liberation Army, FARC factions and criminal gangs - show little progress.
with AP
