The so-called Syrian Observatory for Human Rights said a car rigged with explosives was detonated remotely in the town of al-Shuhayl, close to an oil field, which serves as a base for the so-called Syrian Democratic Forces (SDF).
The Britain-based group added that six members of the Kurdish-led SDF were also killed as they escorted the workers.
Activists with relatives in the area said many of the young men in the blown-up minibus had come from work in the nearby al-Omar field.
No group has claimed responsibility for the attack yet, but it bears the hallmark of attacks carried out by the Daesh Takfiri terror group.
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