BOGOTA (Reuters) - White flags and balloons filled streets nationwide as thousands of Colombians marched on Sunday to express outrage at violence after a car bomb blamed by the government on ELN rebels killed 20 police cadets and injured dozens.

People take part in a rally against violence, following a car bomb explosion, in Bogota, Colombia January 20, 2019. REUTERS/Luisa Gonzalez

President Ivan Duque and other political leaders hugged police officials on route to Bogota’s main Bolivar Square as tearful protesters chanted “no more terrorism” and handed flowers to security personnel.

In last Thursday’s attack, the deadliest in 16 years, a gray Nissan Patrol SUV carrying about 80 kilograms (176 lbs) of high explosive pentolite, broke through checkpoints onto the grounds of the General Santander School in the capital before it detonated, also damaging hundreds of apartments nearby.

Colombia’s National Liberation Army (ELN) rebel group has been blamed for the attack, prompting Duque to request Havana capture and extradite 10 rebel commanders in Cuba for peace talks.

The driver of the car, ELN explosives expert Jose Aldemar Rojas, was also killed in the blast, authorities said.

On Sunday, police officers lined the streets emotionally overwhelmed by the flood of support for their fallen comrades, cadets between 18 and 23 years old.

“It fills my heart to see so many marching and supporting us,” said a tearful Javier Sosa, dressed in olive green uniform.

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Nuns holding white daisies and handkerchiefs marched alongside police singing “a united Colombia will never be defeated.”

The bombing has heightened fears that a new wave of attacks had been launched in the Andean nation as a reaction to the right-wing president’s stance.

Duque, who took office in August, pledged during his election campaign to toughen the fight against the group and drug-trafficking crime gangs that kill and kidnap civilians.

“This is a symbol of patriotism, public spirit and union,” Duque told Reuters as he marched.

“Today we’re here as ordinary citizens to reject terrorism and violence. We’re honoring the memory of those heroes, of those boys who were vilely murdered.”

The ELN, formed by radical Catholic priests in 1964, has not claimed responsibility or issued a public statement, but Duque’s demand to arrest its peace negotiators makes it almost impossible for talks to restart.

Cuba has sidestepped Duque’s request and said it will abide by the rules set out before talks began.

The negotiation protocols provide security guarantees for guerrilla leaders to return to Colombia and protection from military attacks for an agreed period.

Composed of some 2,000 fighters and considered a terrorist organization by the United States and European Union, the ELN began peace talks with the government of former President Juan Manuel Santos in early 2017, but they were suspended by Duque until the group frees its hostages and stops attacks.

The latest incident was the deadliest car bomb attack since the Revolutionary Armed Forces of Colombia (FARC) attacked Bogota’s upmarket El Nogal social club in 2003, killing 36.

Car bombs were frequently used during decades of civil war but the worst of the violence, which killed some 260,000, ended in 2016 when peace was signed with FARC.