Bogotá, February 28 (RHC) -– The National Liberation Army, Colombia's second-biggest guerrilla group, admitted on Thursday it was behind an attack last weekend on the left-wing presidential candidate, but said it was returning fire after being shot at first.

A convoy carrying Aida Avella, a contender from the Patriotic Union party, came under fire on Sunday on a dirt road in the northeastern province of Arauca, where rebels of the ELN have a strong presence.

The ELN, in a statement, said it was attempting to stop the caravan of 12 vehicles with darkened windows to ascertain who was inside but came under fire first.

"We deeply regret the incident and apologize to the candidate Aida Avella. At the same time, we will take the necessary precautions to ensure that this does not happen again."

The government earlier this week blamed the ELN and said police and military intelligence had overheard conversations between rebel members referring to the shots fired.