The UK-based Syrian Observatory for Human Rights said on Sunday that more than 140 people were also injured in Sunday's attack in the suburbs of Deir Az Zor.
The Observatory said that members of the US-backed Syrian Democratic Forces were also killed in the attack that comes days after the eastern city was reportedly captured by the Syrian army.
"The attack took place on the road known as the traders road, which is used to transport food supplies to the areas under the control of the 'Islamic State,'" the group said in a statement.
Those that were targeted in the attack were likely fleeing the fighting that had recently taken place in the city of Deir Az Zor.
The city had almost been entirely controlled by ISIL, also known as ISIS, since 2014. It is the main city of the oil-rich province of the same name.
The campaign to retake the city began in September when Syrian forces managed to break the three-year siege.
On Friday, the Syrian army announced through state media that it had completely recaptured the city from the group.
According to the Observatory, ISIL still controls about 40 percent of Deir Az Zor province.
The Syrian army and Kurdish-led forces supported by the United States are in a race to retake the rest of the eastern province.
The forces of Syria's President Bashar al-Assad have been backed by Russian air raids since September 2015, helping to turn the tide in the war against ISIL and other armed groups.