BEIRUT (AP) — Syrian opposition activists say an explosive device detonated in a northern town held by Turkey-backed opposition fighters killing four people, including two children.

The Britain-based Syrian Observatory for Human Rights said Saturday's car bomb went off at entrance of the industrial district of the town of Azaz.

It added that the explosion occurred near a tanker filled with fuel, causing a fire.

The Aleppo Media Center, an activist collective, also reported four people killed including two children, adding that the explosion occurred inside a shop that sells fuel.

Car bombs have been common since Syria's conflict began in 2011.

Northern Syria has been fraught with clashes between rival insurgent groups including al-Qaida-linked militants and Turkey-backed rebels.