The incident highlights the ongoing security issues in areas controlled by Turkish-backed factions, according to SOHR.
Al-Bab is a town controlled by rebel groups long supported by Ankara.
On Friday several hundred demonstrators gathered in the city protesting signs of a thaw between Ankara and Damascus after their defense ministers met in Moscow for the first time since 2011.
Turkish President Recep Tayyip Erdogan, who in recent years has repeatedly called Syrian President Bashar al-Assad an “assassin,” spoke in November of a “possible” meeting with his Syrian counterpart.
Nearly half a million people have been killed in the Syrian conflict, which has forced around half the country’s pre-war population from their homes.
Turkey has launched successive offensives in Syria since 2016 targeting Kurdish militias as well as Islamic State in Iraq and the Levant (ISIL) militants and forces loyal to Assad.
As a result of these offensives, Ankara and the militia forces it supports have seized swathes of territory along the Syrian border.
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