At least 17 people were killed Sunday in a car bomb near a bustling market and mosque in a rebel-held city in northwestern Syria, a war monitor said.
Four children were among those killed in the explosion in Azaz, at the heart of a Turkish zone of influence in Aleppo province, said the Syrian Observatory for Human Rights.
The attack also wounded more than 20 people, according to the Britain-based monitor.
"Many people were leaving evening prayers when the explosion happened," Observatory head Rami Abdul Rahman told AFP.
In a nearby market, shoppers purchasing clothes and gifts ahead of the upcoming Eid al-Fitr holiday, which marks the end of the Muslim holy month of Ramadan, were also among the victims, said Jihad Berro, a coroner at a local hospital.
He said the medical facility was crammed with victims and their relatives.
"The emergency rooms were full, we placed corpses on the floor," he said.
"It is a real catastrophe before the Eid al-Fitr holiday." Resident Abu Youssef said the explosion torched the neighbourhood.
"The damage is severe: at least six stores were burned, the storefronts of dozens of other stores were blown out," he told AFP.
It was not clear who was behind the attack.
The bombing comes one day after a similar explosion killed 10 people and wounded 20 in the northeastern city of Raqa.
Turkey launched Operation Euphrates Shield in 2016 and seized more than 2,000 square kilometres in northern Syria including Azaz, clearing the area of Islamic State jihadists, while preventing any Kurdish advance in the region.
Ankara keeps Turkish troops and intelligence forces in the area, and still backs the local police forces.