A left-wing rebel group, the National Liberation Army (ELN), was behind a deadly car bombing Thursday in Colombia that killed 21 people at a police academy, the government said Friday.

The attack was the worst to hit the capital, Bogota, in years, injuring 68, including three children.

The assault threatens the already struggling peace talks in Cuba between the government and the rebel group, which has carried out 33 attacks and nine kidnappings since President Iván Duque was inaugurated in August.

Duque responded to the attack by ordering that arrest warrants for 10 ELN members who are part of the negotiating team be reinstated. He called on Cuba to help with their arrests.

“Enough, leaders of the ELN! Colombia says enough!” Duque said in a televised address to the nation Friday night.

For many, the attack brought back memories of the darkest days of narco-trafficker Pablo Escobar’s bombing campaigns and the war against the Revolutionary Armed Forces of Colombia, or FARC. After a peace deal was signed with the FARC guerrillas in 2016, many people were hopeful that the worst of the violence was over, but the bombing Thursday was a reminder that rebel groups like the ELN can still orchestrate attacks far from their areas of control.

Jorge Restrepo of the Conflict Analysis Resource Center said the attack had “sent shock waves not just around Colombia but around the Colombian political institution.”

Selling pink and yellow roses near the El Nogal Club, which saw a devastating FARC bombing in 2003 that killed 36, Elisabet Bolivar, 48, said the attack had left ordinary citizens both “very sad and afraid.”

“They were kids that had nothing to do with this war,” she said of the victims. “The ELN is not interested in peace, not at all. Peace is never going to exist in Colombia.”

The government said the “author” of the attack and driver of the vehicle was a high-ranking member of the ELN who had a history of working with explosives. Prosecutors said a second man, also accused of being an ELN militant, was arrested early Friday in Bogota and would be charged with aggravated homicide and terrorism.

“The ELN are responsible for the terrible attack on the General Santander police academy,” Defense Minister Guillermo Botero said. “We will find those that are responsible for this irrational act, and they will face justice. This crime will not go unpunished.”

The country’s peace commissioner, Miguel Ceballos, said that the attack had been planned for more than six months, adding that “there has been no desire [for peace] on behalf of the negotiating team of this group.”

The driver — José Aldemar Rojas, who went by the nom de guerre “El Mocho” — had spent more than 25 years as an ELN militant, leading some of its armed fronts and heading up its explosives operations, according to Botero. He is believed to have lost his right hand a decade ago while working on the group’s bombmaking operations. Although Rojas had no criminal record, he had been investigated for his role in the ELN. Fingerprints from his left hand were used to identify the body, according to government officials.

The force of the explosion shook the neighborhood, breaking windows in shops and homes that shoulder the academy. Although the General Santander school had a checkpoint and sniffer dogs at its main entrance, Rojas plowed his vehicle through a side entrance, surging past the checkpoint as some motorbikes left the facility. After he was confronted by an officer, he crashed into a wall, detonating the 176 pounds of explosives outside a women’s dormitory. Among the injured were several police recruits from neighboring Panama and Ecuador.

Political analyst Ariel Avila told Caracol television that the latest attack was likely to mean the end of the stalled peace talks between the government and the group. “The peace process with the ELN is dead,” he said. “Today there is no road to negotiation.”

He warned, however, that trying to defeat the guerrilla group, which has operated in Colombia since the 1960s, would be “long and painful.”