The blast in the town of Azaz occurred Sunday as scores of people were leaving the mosque of Maytam, wounding dozens including children, according to the Britain-based Syrian Observatory for Human Rights.
The Observatory said the blast killed at least 14 people. It said the dead included four children.
The Azaz Media Center, a local activist collective, reported at least 13 deaths, along with many others wounded.
The blast occurred after the "iftar" meal that breaks a daylong fast during the Muslim holy month of Ramadan. The attack came a few days before Muslims celebrate the end of the holy moth with Eid el-Fitr, one of Islam's most important feasts.
The town, which was once controlled by rival Kurdish fighters opposed to Turkey, has been hit by similar attacks in the past.