An early morning bomb attack outside a police station in Colombia's coastal city of Barranquilla killed at least 5 police officers and wounded 42 on Saturday, authorities said.
The attack targeted the officers as they gathered in the San Jose neighborhood to receive their orders for the day in what police denounced as an "act of barbarity."
A reward of 50 million pesos (about $18,000) was offered for information leading to the perpetrators.
"We think it could be retaliation by these groups who have recently been greatly impacted," metropolitan police commander Brigadier General Mariano de la Cruz Botero said in comments broadcast by Caracol Radio, referring to crime gangs active in the port city.
Botero said one person had been arrested in connection with the bombing, and that police suspect others were involved. The person in custody could be the individual who placed and then triggered the device, he said.
President Juan Manuel Santos sent his condolences to the families of those killed and injured, and said on Twitter that the government would not rest until those responsible were brought to justice. Mexican President Enrique Pena Nieto also tweeted his condolences.
Colombia has myriad crime gangs, some which operate across large swaths of rural territory and others in major cities. Many are involved in the production and trafficking of cocaine, largely to the United States and Europe, as well as extortion and other crimes.