The Syrian Observatory for Human Rights in Britain said the blast occurred when people were leaving a mosque in Azaz after the iftar meal that breaks a day-long fast during the Muslim holy month of Ramadan. The observatory said 14 people, including four children, were killed in the blast.
The Azaz Media Center, a local activist collective, reported 13 deaths and several others wounded.
Azaz, which is now held by Turkey-backed fighters, was once controlled by Kurdish fighters opposed to Turkey.
The blast in Azaz comes a day after 10 people were killed in a suicide car bomb attack in Raqqa, a former stronghold of the Islamic State group in north Syria. The explosion killed five civilians and five soldiers of the Syrian Democratic Forces, a Kurdish-Arab alliance backed by the United States that wrested the city from the Islamic State in October 2017, AFP had reported.