AZAZ, Syria

At least four people were killed and 20 injured late Saturday in a car bomb attack that rocked a bustling market in Syria's northern city of Azaz, according to local sources.

The attack in the heart of Azaz's vibrant marketplace was in an area controlled by opposition forces.

Initial assessments are treating the explosion as a terror attack.

Following the attack, the injured were transported to the Azaz Hospital, while security forces intensified security measures in the surrounding area.

Security forces have initiated an investigation into the attack but so far no group has claimed responsibility for the attack.