Colombia's second largest guerrilla group, the National Liberation Army (ELN), apologized Monday for killing two workers sent to repair an oil pipeline that had been bombed by the group.

Guerrilla snipers shot the two men on September 14 as they worked to repair a bomb-damaged section of the Cano Limon Covenas pipeline near the town of Teorama in the department of Norte de Santander, authorities said.

In a statement posted on its website, the ELN acknowledged it had blown up the pipeline.

"In subsequent events, two workers of the contracting company in charge of repairing the pipeline died," it said.

"We ask forgiveness of their families and relations," it said, blaming the killings on "personal errors of the commander in charge of these actions."

The Colombian Defense Ministry had denounced the killings as "atrocities that violated all norms of international humanitarian law and the rights of man."

A pillar of the economy, the oil industry has been one of the chief targets of the country's two main guerrilla groups, the FARC and the ELN, which have entered into peace negotiations with the government.

After a period of booming growth in 2012 and 2013, oil production has declined somewhat in Colombia, in part because of attacks by the guerrillas, who accuse the oil companies of plundering the country's natural resources.