The smaller of Colombia's two main guerrilla groups apologized on Thursday for an attack last weekend on the motorcade of Aida Avella, presidential candidate of the leftist Union Patriotica.
No one was hurt in the shooting.
"We deeply regret this incident and we apologize for it to candidate Aida Avella, at the same time that we will take the necessary measures so that such deeds do not occur again," the National Liberation Army, or ELN, said in a communique.
An ELN unit asked vehicles "with dark windows" making up the UP caravan to stop, as they do with all such vehicles traveling on secondary roadways in the "zone of continuous confrontation" in the northeastern province of Arauca, the statement said.
"Instead of stopping, from the inside of one of the vehicles they fired several times at the guerrillas, who had to take cover so as not to be affected and, in reply, fired some shots with a handgun," the ELN said, confirming the account provided earlier by the Defense Ministry.
The incident occurred on Sunday on a highway in the rural part of the municipality of Tame, near the border with Venezuela.
Avella said at the time that "militaristic forces" were responsible for the attack, but the Defense Ministry blamed the ELN.
The attack sparked great outrage in Colombia that revived memories of the extermination of the UP in the 1980s and '90s when more than 4,000 militants and leaders of that group were killed after agreements were struck between the government and the FARC, the Andean nation's largest insurgency.
Avella returned to Colombia in late 2013 to head the presidential candidacy of the reborn UP after 17 years of exile in Switzerland following a failed attack on her life.
The Colombian government and the FARC are currently engaged in peace talks. EFE