BOGOTA - The National Liberation Army, a leftist Colombian rebel group known as ELN, has declared a 72-hour armed lockdown in areas where they operate, restricting transport and commerce amid signs of further delays in their efforts to begin peace talks.

The lockdown begins on Sunday, said the ELN, which the United States and European Union consider a terrorist group.

"We have directed all the combatant forces of the National Liberation Army to take part in an armed strike," the country's second-largest rebel group said in a statement on its website on Friday.

During similar lockdowns in the past, rebels have forced shops to close and buses to halt transport along routes.

The ELN has been holding preliminary peace talks with the government of President Juan Manuel Santos for more than two years, but formal negotiations have yet to begin.

Each side has blamed the other in recent weeks for ongoing delays at these talks. Santos has said negotiations will not start until the group frees two hostages.

The stoppage of commercial activities and transport was being held to mark the 50th anniversary of the death of rebel hero Camilo Torres, a radical Catholic priest killed in combat, the group said.

"We emphasize that our actions are not against civilians, and we ask them for prudence while the armed strike takes place," the ELN said.

The group has battled a dozen governments since it was founded in 1964. It has continued kidnapping and attacks on infrastructure even during the exploratory talks.

Officials blamed the ELN for a bombing this week on the Cano Limon oil pipeline.

The government looks set to sign a peace deal with larger rebel group the Revolutionary Armed Forces of Colombia, or FARC, in the coming months.

FARC leaders said on Monday, however, that peace in Colombia would be "incomplete" if the ELN, which has about 2,000 fighters, does not participate in negotiations.