A car bomb struck a convoy of an Iraqi private security firm in Baghdad on Thursday, killing at least four people and wounding 11 others, a police source told Xinhua.

The attack occurred in the morning when a booby-trapped car went off near a convoy of sport utility vehicles (SUV) used by an Iraqi private security firm, in Baghdad's western district of Mansour, the source said on condition of anonymity.

The powerful blast set ablaze one of the convoy's SUVs and caused damages to several nearby cars and buildings, the source said.

Violence and sporadic high profile attacks are still common in Iraqi cities despite a dramatic decrease of violence in general over the past few years.