BOGOTA, Colombia (AP) — Colombia is pressuring Cuba to turn over leaders of the South American nation's last remaining rebel group who had been on the island for peace talks that have been stifled by the bombing of a police academy that left 21 dead.

The National Liberation Army claimed responsibility Monday for the car bombing, stating the attack against a military installation was a legitimate response to the armed forces' bombing of a guerrilla camp during a recent unilateral ceasefire.

"It is permissible within the laws of war," the guerrilla army said in a statement. "There were no non-combatant victims."

High Commissioner for Peace Miguel Ceballos responded hours later by urging Cuba, the host of peace talks that began under the previous president, to capture the group's leaders, warning that failing to do so would violate international accords.

"The ELN had a great opportunity to show its will for peace," Ceballos said at a press conference, referring to the group by its Spanish initials. "And it didn't do that."

Authorities say a one-armed explosives expert belonging to the rebel group carried out the bombing Thursday morning, driving in through a side gate with 80 kilograms (175 pounds) of pentolite.

President Ivan Duque asked Cuba to arrest 10 rebel commanders who have been living on the communist-governed island with his permission in hopes of jumpstarting stalled peace talks. Cuba, which condemned the attack, has pushed back, saying it is obliged to follow the protocol used by Duque's predecessor, Juan Manuel Santos, allowing the negotiators to leave the island in the event of a rupture in talks.

"Cuba has never allowed, nor it will ever allow, its territory to be used for the perpetration of terrorist actions against any state," Cuban Foreign Minister Bruno Rodriguez wrote in a tweet. "Cuba has strictly complied with its role as guarantor and alternative venue of the peace dialogue between the Colombian government and the ELN."

Ceballos said Monday that the peace talk protocol was established by Colombia's previous presidential administration and therefore holds no weight. He said that rather than treat the incident as a rupture in dialogue, officials on the island should cooperate in ensuring all those responsible for a terrorist attack are held accountable.

According to the protocol, a copy of which was obtained by The Associated Press, Colombia's military should cease all activity in certain hotspots over a 72-hour period to facilitate the safe return of the ELN leaders. The document also leaves open the possibility of the rebels transiting through Venezuela.

"We can't allow those responsible for this terrorist attack to return to the ranks of the ELN and hide from justice in the jungle," Ceballos said.

Last week's attack against the General Santander police academy was the deadliest in Colombia in 15 years and reminded many of the bloodiest chapters of the nation's war between leftist rebels, paramilitaries and the state.

Santos began peace talks with the ELN in hope of reaching an agreement like that achieved with the former Revolutionary Armed Forces of Colombia. But from the start, the talks were fraught with difficulty, with Santos temporarily suspending the talks a year ago after a series of bombings that killed seven police officers.

Since his election last year, Duque has vowed to continue peace talks only if the ELN rebels hand over all kidnapping victims and cease violence.

In their statement, the ELN said it wants talks to continue.

"President Duque, we want to reiterate that the path of war is not the future of Colombia," they wrote. "The best thing for the country is to send your delegation to the peace talks to continue the process."