It was the first such attack attributed to the ELN (National Liberation Army) since it resumed peace negotiations with the government earlier this month.

The army did not say when the attack, which also injured four other soldiers and a civilian, took place.

The ELN and the government agreed on November 7 to resume peace talks that were stalled for several months after an attack on a military base that killed three soldiers and injured 28.

A ceasefire was not part of that agreement, however, and a week after the parties agreed to resume talks, the military killed 13 guerrillas in two operations.

The ELN is the biggest of the armed groups still active in Colombia since the government signed a deal with the much bigger FARC Marxist rebel group, which disarmed in 2017 after more than 50 years of war with the state.

The deal with FARC sought to end the longest-running war in the Americas, but holdout FARC splinter groups and the ELN have refused to make peace.

Leftist guerrillas, right-wing paramilitaries, drug gangs and state forces remain in open conflict in parts of the country, despite President Gustavo Petro opening negotiations in a quest for "total peace."

The government condemned the latest attack Thursday, accusing the ELN of "talking about peace while making war."

The Norwegian Refugee Council (NRC), a humanitarian organization, said Thursday that at least 1.5 million people have been displaced in Colombia since the deal with the FARC in 2016.

"If displacement was a thermometer of peace, then Colombia's health would be failing," NRC's Colombia country director Giovanni Rizzo said in a statement.