A car blast in a town controlled by Turkish-backed Syrian rebel groups near the Turkish border killed at least four people on Saturday, a war monitor and local media reports said.
The town of Azaz lies in a part of northern Syria that Turkey's army helped rebels fighting President Bashar al-Assad to capture in 2016.
The Syrian Observatory for Human Rights war monitor said the explosion happened in an industrial area of Azaz.
The number of dead is likely to rise, it said, because other people were seriously injured.
In recent weeks there have been a number of blasts in the parts of north-west Syria along the border where Turkey trains and pays for a unified armed force of Syrian rebels.
Northern Syria has become a haven for large numbers of displaced people who have sought refuge from fighting elsewhere in the country, or who do not want to live under Assad.