The Colombian rebel group National Liberation Army (ELN) has claimed responsibility for a terrorist bombing of a crowd near an iconic Bogota landmark.

The bombing occurred last week, and left 25 civilians wounded and one security personnel dead. While originally denying ELN involvement, the group later took responsibility.

The attack frustrates an already tenuous peace negotiation effort between the Colombian government and the rebel group, which have been ongoing in neighboring Ecuador.

In a statement released Monday, the group said that a “bilateral cease-fire must be declared to avoid any future attacks and give space to recently launched peace talks.”

The Colombian government has engaged in decades of peace talks with the various rebel factions operating in the country. Notably, President Juan Manuel Santos negotiated a successful peace agreement with the FARC last year, ending decades of war which killed thousands, and earning a Nobel Peace Prize along the way.

It was common for frequent starts and stops to occur during those negotiations, as rebels and the government would exchange attacks as reprisals for the others’ actions.

This bombing in Bogota, while likely an attempt by the ELN to strengthen its hand in negotiations aimed at an eventual cease-fire, have outraged political opposition, who insist the government must now break off talks once again.

The ELN is a political revolutionary group, with roots in a mix of Marxist-Leninist and nationalist ideologies. It has been engaged in an armed resistance against the Colombian government since 1964, and is reportedly composed of around 2,500 fighters, down from a height of 5,000.