Canadian miner Continental Gold said on Thursday three of its geologists were killed in northern Antioquia province in Colombia in an armed attack.
Three others were also injured in the attack, a company spokesman told Reuters.
The incident took place in the village of Ochali in the municipality of Yaramul, Antioquia, which is located within the boundaries of Continental's Berlin project, the company said in a statement.
The Colombian army said in a statement one person was missing after the incident, which it said was carried out by former members of the Revolutionary Armed Forces of Colombia (FARC) rebel group, which demobilized last year under a peace deal.
Some 12 000 FARC members, including 6 000 combatants, demobilised under the accord and the group is now a political party. However, more than 1 200 former FARC fighters did not lay down their arms and instead founded new groups dedicated largely to drug trafficking and illegal mining.
Energy installations and projects in the Andean country, especially oil pipelines, are regularly targeted by bombings and other attacks by rebels and dissidents.
Thursday's attack was the second on Continental staff in as many weeks.
One engineer died and another was wounded on September 5 after they were shot at while traveling near the company's Buritica mine.