A car-bomb attack that killed two people and left 15 others injured was planted by leftist rebels, Mayor Jorge Ospina of the Colombian city of Cali said Monday, dpa reported.
General Gustavo Ricaurte, the Cali police commander, directly blamed "FARC terrorists" for the attack that happened late Sunday.
Just hours earlier, the Revolutionary Armed Forces of Colombia (FARC) had freed four hostages, fulfilling the Marxist insurgent group's promise of a unilateral release.
The three police officers and one soldier, who had been held since 2007, were handed over at an undisclosed site in jungles in southern Colombia by FARC members who met with a delegation from the International Committee of the Red Cross and other non-governmental organizations.
FARC has said it intends to release another hostage on Monday, the former governor of Meta province, Alan Jara, and another on Wednesday, former Colombian parliament member Sigifredo Lopez.
The attack late Sunday was perpetrated by an alleged rebel who crashed the car he was driving against an administrative police facility in central Cali - the third-largest city in Colombia - and then exchanged shots with officers who attempted to arrest him.
Shortly afterwards, the 70 kilogrammes of explosives that were in the vehicle were detonated and caused great damage within a radius of some 200 metres.
The authorities said the alleged rebel was killed in the incident, along with an old man who was at a nearby shop. Among the injured were three police officers and seven minors who live in the area.
"It is the most radical sectors within the rebel camp that have perpetrated this attack," Ospina said.
The attack happened in a poor neighbourhood in the city in the south-western Colombian province of Valle del Cauca.