Leftist guerrillas detonated an explosive charge under a military vehicle, killing three soldiers in northern Colombia, the military said.

Two others were injured in the attack Sunday in Norte de Santander, which borders Venezuela, but they were evacuated and were "out of danger," the army said in a statement.

The attack was attributed to the National Liberation Army, or ELN by its Spanish initials, Colombia's second largest guerrilla group.

It came a day after three guerrillas were killed in clashes with the army in northern Colombia.

The ELN has been in preliminary talks with the government about entering into peace talks, but fighting persists.

The country's largest guerrilla group, the Revolutionary Armed Forces of Colombia, or FARC, have been in peace talks in Havana since November 2012.

The FARC currently is observing a unilateral ceasefire, even though the government of President Juan Manuel Santos has refused to reciprocate until a comprehensive peace agreement is reached.

The peace talks are seen as the best chance yet for ending a 50-year-old conflict that is estimated to have claimed some 220,000 lives.