A car bomb blast has killed four people and wounded around 20 in front of the palace of justice in the Colombian city of Cali, officials say.

Victims were pedestrians, a taxi driver and his passengers in the center of the city about 186 miles southwest Bogota.

"It has been an attack, a terrorist attack because civilians have died," mayor of Cali Jorge Ivan Ospina told radio station Caracol on Monday.

There was a police officer among the people injured, officials said.

Authorities are investigating the attack and weighing a possible reward for information leading to the attackers.

No one has claimed responsibility for the explosion yet.

Earlier in mid August, four civilians were killed and dozens wounded in a bomb explosion in Iturango town.

AGB/DT