BOGOTA: Leftist killed 12 security officials on Monday even as the government pushes for a peace deal with the larger FARC guerrilla force, President Juan Manuel Santos said.

Authorities attributed the attack to the National Liberation Army, or ELN, Colombia’s second-biggest rebel group. The poll workers were transporting to the capital for counting about 130 ballots cast at the remote U’wa reservation during Sunday’s elections for governors, mayors and other local officials.

“My heart really is broken,” Santos said. “This shows that the ELN does not understand that this is peace time, and not time for war.”

The president warned he had ordered the Defense Ministry and the military to “step up” anti-ELN operations.

Of those killed early Monday, 11 belonged to the army while the other was a police officer. Three more soldiers were wounded and six people remain missing, including two poll workers and an indigenous guide, Defense Minister Luis Carlos Villegas said.

“They were safeguarding the political liberty of our U’wa brothers,” Villegas said in a press conference, adding that the military’s top command had traveled to the area to oversee efforts to locate those still missing as well as the attackers.