At least four police officers were killed and another 42 injured when a homemade bomb exploded early Saturday outside a police station in the Colombian city of Barranquilla hours after a high-powered car bomb gutted another police station near the border in neighbouring Ecuador.

The two attacks didn’t appear to be related, but they underscore the security challenges that have emerged since a 2016 peace deal with the Revolutionary Armed Forces of Colombia, which long played a dominant role in South America’s drug trade.

The blast in Barranquilla, redolent of some of the worst violence at the apex of Colombia’s drug violence three decades ago, took place shortly after 6:30 a.m. local time as officers were lining up in formation at the police station’s patio following a shift change.

Gen. Jorge Nieto visits a police officer wounded in the attack on a station in Barranquilla. (Colombia National Police/Handout via Reuters)

Brig.-Gen. Mariano Botero, head of Barranquilla’s police, said the attack may have been carried out by associates of a local crime boss known as “Happy,” who was arrested recently on charges of drug trafficking, extorting businesses and terrorizing residents with threats of murder in the Caribbean city.

“For us there’s no doubt this was an act of retaliation,” said Mayor Alejandro Char, appealing for calm amid reports that other attacks were being planned. “We’re not going to allow a few bandits to disturb the peace of Barranquilla.”

1 suspect arrested

Images circulating on social media show several officers being treated for injuries while laid out on the rubble and blood-strewn ground. Char said one suspect had been arrested and two more identified.

Authorities offered a $18,000 US reward for information on those responsible for the attack.

Barranquilla’s Mayor, Alex Char, centres, arrives to the police station in San Jose district, in Barranquilla. (Jorge Payares/EPA-EFE)

Colombia’s peace deal has emboldened new criminal groups that have proliferated since the rebels disarmed last year as part of a peace deal ending a half-century conflict. The rebels long funded their insurgency by playing a dominant role in Colombia’s criminal underworld and their retreat has left valuable drug smuggling routes up for grabs.

The former rebels, whose new political party was kicking off its campaign for Colombia’s presidency on Saturday, expressed their “radical condemnation” of the attack against their former battlefield enemies.

Several Colombian police investigators search for evidence outside the police station. Barranquilla’s mayor said one suspect had been arrested and two more identified. (Jorge Payares/EPA-EFE)

“Colombia needs to make an enormous collective effort to emerge from the swamp of violence, death and fear,” the former rebels said in a statement.

President Juan Manuel Santos also condemned the attack, saying on Twitter, “We won’t rest until we find those responsible.”

Another car bomb in nearby Ecuador

In a separate, apparently unrelated incident, a car bomb exploded after midnight Friday outside a police station in Ecuador, near the border with Colombia. The powerful blast, which residents at first thought was an earthquake, gutted a three-story police station in the border town of San Lorenzo and destroyed several adjacent homes.

At least 13 police officers were being treated for light wounds.

The scene of the bomb explosion at the police station is seen in San Lorenzo, Ecuador on Jan. 27, 2018. At least 13 police officers were being treated for light wounds. (Ecuador Ministry of Interior/Handout via Reuters)

Authorities had yet to identify anyone responsible for the attack, but immediately looked across the border for clues.

“We will not permit armed group in our territory,” said Gen. Ramiro Mantilla, head of Ecuador’s police.

While political violence from Colombia has long had spillover effect on northern Ecuador such attacks in the far-more-peaceful nation are rare.