HAVANA (AFP) - Colombia's leftist National Liberation Army (ELN) rebels claimed responsibility on Monday (Jan 21) for the bombing of a police academy in Bogota that killed 20 people as well as the attacker, and derailed peace talks being held in Havana.

The ELN said last Thursday's (Jan 17) car bombing, which sparked nationwide protests, was a reprisal attack after the government of President Ivan Duque failed to respect a unilateral ceasefire declared by the rebels over Christmas.

"The operation carried out against these installations and troops is lawful within the law of war, there were no non-combatant victims," the ELN said in a statement on its website.

It added that the academy was a military installation where cadets received training to become intelligence operatives and conduct military operations.

"The president did not respect the gesture of peace" and "his response was to carry out military attacks against us", it said.

Specifically, the ELN said Colombian troops bombed a camp on Dec 25, affecting a family of peasants who were nearby.

"It is then very disproportionate that, while the government is attacking us, we cannot respond in self-defence," the statement added.

The attack was a major setback to two years of peace talks with the ELN - hosted first by Ecuador and currently by Cuba - that failed to go beyond the exploratory stage before stalling when Mr Duque took power in August 2018.

In its wake, Mr Duque announced that he was reinstating arrest warrants for 10 ELN members who are part of the group's delegation to the Cuba talks and said he was revoking "the resolution creating the conditions that allow their stay in that country".

Thousands of people marched throughout Colombia on Sunday to condemn the car bombing, the deadliest attack with explosives in Bogota since 2003.

Protests were held in several cities around the country, with marchers in white waving Colombian flags and chanting slogans like "cowardly killers" and "life is sacred".

The peace talks had been aimed at ending more than five decades of insurgency by the Marxist-inspired guerrillas.

Colombia has experienced several years of relative calm since the 2016 peace accord signed by then-president Juan Manuel Santos and the Revolutionary Armed Forces of Colombia (FARC) guerrillas.

With the landmark agreement turning the former rebels into a political party, the smaller ELN is considered the last active rebel group in the country.