MEXICO CITY (Sputnik) - The Colombian National Liberation Army (ELN) on Monday claimed responsibility for the deadly attack on a police school in Bogota, which left 21 people killed and 68 others injured last week.

On Thursday, a bomb-laden car broke through a checkpoint near the police academy building and exploded on its premises. The authorities announced a three-day mourning period in light of the deadly attack, blaming it on the ELN. On Saturday, Colombian President Ivan Duque said that he ordered to remove the suspension of the arrest warrants for ten ELN members who were part of the rebel delegation at the peace talks with the government.

"The operation against this institution and the military is lawful within the law of war, there were no civilian casualties," the ELN statement said in a statement, as quoted by the Globovision news outlet.

According to the militants' statement, the police school is a military facility, where personnel was being trained to "wage war against social protest." The ELN added that the attack came as response to the refusal of Duque to respect the Christmas ceasefire. The statement pointed that the Colombian military on December 25 shelled an ELN camp injuring a peasant family, which was nearby.

On December 17, the ELN announced that the militants would unilaterally cease all offensive operations from December 23 to January 3 on the occasion of the Christmas and New Year's celebrations.

READ MORE: Colombian Defence Min.: ELN Rebels Behind Car Bomb on Police School in Bogota

The ELN, a group that follows communist ideology and believed to have around 1,500 fighters, has been engaged in an armed struggle with Colombian authorities with the aim of overthrowing it since 1964. After the Revolutionary Armed Forces of Colombia disarmed itself in 2017, the ELN became the country's only guerrilla movement. In February 2017, the armed group started peace talks with the Colombian government, which have yet to yield concrete results.