Colombia's ELN guerrillas have kidnapped a mayor's father, the army said Friday, calling it an act of terrorism that damages peace talks with the country's last active rebel group.

Army commander Alberto Mejia blamed the leftist guerrillas for the disappearance of Cristo Contreras, whose son Edwin is the mayor of the town of El Carmen in the restive northwestern region of Catatumbo.

He said the rebels had also bombed an oil pipeline in the same region, the scene of frequent ELN attacks.

"We are reporting two acts of terrorism by the ELN in Catatumbo," the general told a press conference.

"Such messages do a lot of damage to the (peace) process and of course cause it to lose legitimacy. The government is reaching out a hand to them, and this is how they respond."

Colombian President Juan Manuel Santos is trying to negotiate a peace deal with the ELN to match the historic accord his government sealed last year with the FARC guerrillas.

Both the FARC, or Revolutionary Armed Forces of Colombia, and the ELN, or National Liberation Army, launched uprisings against the state in 1964.

The multi-sided conflict has killed 260,000 people and left 60,000 missing.

Peace talks with the ELN opened on February 7, but have gotten off to a rocky start over the rebels' refusal to renounce kidnapping -- a tactic they have used to get ransom money and exact revenge on political enemies.

The talks were originally due to open in October, but the ELN's refusal to release its most high-profile hostage -- ex-lawmaker Odin Sanchez -- made Santos call them off.

A flurry of behind-the-scenes negotiations followed, leading to Sanchez's release on February 2 in exchange for two ELN prisoners.

The latest kidnapping allegation -- which drew no immediate response from the ELN -- could place new pressure on the talks.

Mejia said Contreras disappeared Thursday from his ranch in Catatumbo, a remote region near the Venezuelan border.

The attack on the Cano Limon-Covenas oil pipeline ocurred the same night, he said.