The commander for the region where Saturday's incident occurred says the soldiers were killed by explosives. Gen. Hernan Giraldo tells reporters that return fire by troops killed three guerrillas and wounded two.
The general has given no other details of the fight in a rural area near Colombia's Pacific Coast about 400 kilometers (250 miles) northwest of Bogota.
An attack blamed on the FARC last month killed 11 soldiers near the border with Venezuela. The Colombian military responded within days with airstrikes on two FARC camps that killed more than 60 rebels.