The bomb exploded at a police academy in capital Bogota, wounding dozens others in what the authorities condemned as "terrorism". Defence Minister Guillermo Botero blamed the attack on leftist rebel group.
Colombia's ELN rebel group was responsible for the car bomb attack against a police academy that killed at least 21 and injured dozens, President Ivan Duque said on Friday, making it almost impossible peace talks with the insurgent group can soon restart.
He called on Cuba to capture 10 National Liberation Army (ELN) commanders who are currently in Havana for the stalled peace talks.
In Thursday's attack, a car broke through checkpoints onto the grounds of the General Santander School in the capital Bogota before it detonated, shattering windows of apartments nearby. Defense Minister Guillermo Botero said on Friday the car was driven by ELN explosives expert Jose Aldemar Rojas.
"The ELN armed terrorist group is the author of this despicable attack. This was an attack prepared and organized many months in advance. For all of Colombia today it is clear that the ELN has no genuine will for peace," Duque said in a televised national address.
At least 20 police cadets died in the blast, as did Rojas, authorities said.
ELN has been stepping up attacks on police targets in Colombia amid a standoff with the conservative government over how to re-start stalled peace talks.
Made up of some 2,000 fighters and considered a terrorist organisation by the United States and European Union, the group began peace talks with the government of former President Juan Manuel Santos February 2017 but they have been put on hold by President Ivan Duque.
Revised death toll
Earlier police revised the death toll from 11 to 21.
"Unfortunately, the preliminary toll is 21 people dead, including the person responsible for the incident, and 68 wounded," the police said in a statement, adding 58 of those injured had been discharged from hospital.
Earlier, reports said the scene outside the police academy was chaotic, with ambulances and helicopters rushing to the tightly-controlled facility.
There was no immediate claim of responsibility but the Colombian authorities named the man they suspect of carrying out the bombing, who also died in the explosion.
TRT World's Arabella Munro has more.
Attorney general Nestor Humberto Martinez said Jose Aldemar Rojas Rodriguez was "the material author of this abominable crime," adding that the vehicle used in the attack contained 80 kilograms of explosives.
TRT World spoke with Colombian journalist Richard McColl, who said the blast has "severely wounded" many police cadets.
'I don't have any information about my son'
Rafael Trujillo said he was delivering a care package to his son Gerson, who entered the school two days ago, when he was stopped in his tracks by the blast a block away from the school's heavily fortified entrance
"I'm sad and very worried because I don't have any information about my son," said Trujillo, standing outside the facility, where police officers had set up a taped perimeter.
"This reminds me of some very sad days in the past."
Early images from the City TV station showed ambulances moving around the area close to the school in the south of Bogota.
Witnesses said they heard a loud explosion that destroyed windows in adjacent buildings.
Penalosa called it a "terrorist act" without naming who was behind the bombing.
Pictures on social media showed a charred vehicle surrounded by debris on the academy's campus.
President Ivan Duque, who was visiting a western state, was rushing back to the capital to oversee police operations.
"All of us Colombians reject terrorism and are united in confronting it," Duque said in a tweet. "We won't bend in the face of violence."
Focus on leftist rebels
For decades, residents of Bogota lived in fear of being caught in a bombing by leftist rebels or Pablo Escobar's Medellin drug cartel.
But as Colombia's conflict has wound down, and the nation's largest rebel group disarmed under a 2016 peace deal, security has improved and attacks have become less frequent.
Photo shows site of explosion that took place today at bogota police academy shows small vehicle in flames. Authorities suspect it was a car bomb pic.twitter.com/6fSbbtz3bl— manuel rueda (@ruedareport) January 17, 2019