The fighting occurred yesterday in the town of El Doncello, in the department of Caqueta, a stronghold of the southern bloc of the Revolutionary Armed Forces of Colombia, the military statement said.
Three soldiers were injured and two militants were captured.
The latest casualties of Colombia's almost half century old insurgency came a day after the rebel group announced it had captured a US-ex soldier, but said it was ready to release him as a gesture toward peace talks with the government.
Talks between the rebels and the government opened last November in Cuba, in the fourth attempt since the 1980s to end the conflict that has left 6,00,000 dead, more than 3.7 million displaced and 15,000 missing.