Minister Pedro Sanchez huddled with top security officials in the tropical city of Cali, where a truck bomb exploded on a busy street killing six and wounding 60 on Thursday afternoon.

Although the vehicle-mounted cylinder bombs detonated near a military aviation school, all of the victims were civilians, the authorities said.

"All of a sudden, something incredibly powerful exploded and everyone fell to the ground," eyewitness Jose Burbano told AFP.

Just hours earlier, guerrillas in the northwest of the country used rifles and drones to down a police helicopter, leaving 13 officers dead.

Despite the attacks, Sanchez claimed the military was making inroads against armed groups on several fronts.

"The impact on criminal groups has been to drive them to a state of desperation" he said.

Sanchez said that in five areas of operation, extortion, murders and child recruitment had fallen, so "they attack with the most criminal and insane weapon that exists: terrorism."

President Gustavo Petro's leftist government has blamed both attacks on guerrilla groups that split from the once-powerful Revolutionary Armed Forces of Colombia (FARC) in rejection of a 2016 peace accord.

"We are facing an international mafia, with armed gangs here," Petro said around midnight Thursday.

But he is facing mounting questions about security failings, and his strategy of engaging rather than fighting armed groups.

"This is an intelligence failure that has to be corrected," Cali mayor Alejandro Eder told local radio Friday, revealing that a second truck bomb had failed to go off.

"If both had exploded, the situation would have been infinitely worse" he said.

Police said they had taken one of the suspected attackers into custody after he was apprehended by the public at the scene.

Named only as "Sebastian," the man was said to be a member of the Central General Staff (EMC) dissident guerrilla group.

- 'Climate of fear' -

Colombia's 2016 peace deal brought relative tranquility to the country after decades of armed conflict that had killed hundreds of thousands of people.

But it also spurred an alphabet soup of dissident guerrilla groups, paramilitaries and cartels that rejected peace and continue to vie for control of territory and the lucrative cocaine trade.

Guerrillas have been blamed for dozens of recent attacks, including the assassination of a conservative presidential candidate, which have left Colombians wondering whether this is a return to the bad old days.

Laura Bonilla, an analyst with the Peace and Reconciliation Foundation, said dissident groups were trying to "destabilize the country."

"What they want is to put the government on the ropes and generate a climate of fear that has a lot to do with the 2026 elections," she told AFP.

Next May, Colombia will elect a new president. Petro, who has led the country's first-ever leftist government, is constitutionally barred from running again.

Security, along with bread and butter economic issues, looks set to dominate the campaign.

Petro's critics accuse the left of giving armed groups the space to reorganize and grow, while neglecting costly intelligence operations that had helped bring down the FARC.

Under Petro, Colombian cocaine production, which funds many rebel operations, has hit record highs according to the United Nations Office of Drugs and Crime.