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.

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 kg (176 lbs) of the 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.