'This tragedy should have never occurred': Colombia admits role in killing activists

Colombia's president has asked forgiveness for the state's role in the systematic killings of leftist activists in the 1980s as the South American nation starts coming to grips with its bloody past ahead of the signing of a historic peace deal with Marxist rebels.

President Juan Manuel Santos made the apology Thursday at a solemn ceremony at the presidential palace attended by surviving members of the Patriotic Union, some wearing shirts in the party's yellow colours with the slogan "They can cut the flowers, but they can't stop the birth of spring."

Some 3,000 members of the short-lived political party set up in the 1980s during peace talks with the Revolutionary Armed Forces of Colombia were slain by paramilitary death squads, sometimes in collaboration with state security forces, in little under a decade. Those killed during what Colombians commonly refer to as political "genocide" included two presidential candidates, lawmakers and countless local officials.

"This tragedy should have never occurred," Santos said, recognizing that a weak state then overwhelmed by powerful drug cartels and their ties to leftist insurgencies was unable to provide the most basic political protection.

"The persecution of members of the Patriotic Union was a tragedy that led to its disappearance as an organization and caused untold damage to thousands of families and our democracy," Santos said.

While expressing regret for the state's past negligence, Santos said that Colombia had made great strides opening political space for the democratic left, a challenge in a country with a recalcitrant guerrilla movement despised by wide segments of society.

In less than two weeks, he'll sign a historic peace deal reached with the FARC that if ratified in a nationwide referendum will pave the way for thousands of rebels to turn over their weapons and compete at the ballot box with traditional parties.

Evidence of the transformation, he said, is that under the peace deal the FARC leaders will entrust their protection to state security forces.

But Aida Avella, who spent a long exile in Switzerland after surviving an attempt on her life and is now the party's leader, said changing conservative Colombians' attitudes will take longer.