A car bomb on Tuesday killed five people, mostly local police, on the outskirts of the Turkish-controlled town of Al-Bab in northern Syria, a war monitor said.
The explosion, which targeted a police station, killed a police chief from another district, two officers and two civilians, the Britain-based Syrian Observatory for Human Rights reported.
It also wounded 19 others, the monitor added.
There was no immediate claim of responsibility for the car bombing, but there has been a string of attacks in Al-Bab since its capture by Turkish troops from the Islamic State group in 2017.
Observatory head Rami Abdul Rahman said it was "likely that sleeper cells of the Islamic State group" were behind the attack.
Turkey and its Syrian proxies control several pockets of territory on Syria's side of the border following three military incursions since 2016.
Al-Bab, 40 kilometres (25 miles) northeast of Syria's second city Aleppo, was one of the western-most strongholds of the jihadists' self-styled "caliphate".
US-backed Kurdish forces seized the last scrap of that territorial proto-state from the jihadists in eastern Syria in March last year.
But the jihadist group continues to carry out attacks through a network of sleeper cells operating in some regions it used to control.
Syria's civil war has killed more than 380,000 people since it started with the repression of anti-government protests in 2011.