The attack took place at near the border of Deir Ezzor and Hasakah provinces, and the dead included civilians fleeing the fighting in Deir Ezzor, Syrian Observatory for Human Rights said.
A car bombing targeting displaced Syrians in the northeastern province of Hasakah on Thursday killed at least 18 people, a war monitor said.
The Britain-based Syrian Observatory for Human Rights (SOHR) said the attack was carried out by Daesh and took place in an area where Syrians displaced from Deir Ezzor province usually gather.
Observatory head Rami Abdel Rahman said "at least 18 people, including displaced persons were killed".
Two separate offensives targeting Daesh are underway in the eastern oil-rich province of Deir Ezzor, one by Russia-backed regime forces and the other by US-backed Syrian Democratic Forces (SDF).
Earlier Thursday, SOHR, which relies on a network of sources inside war-torn Syria, said regime forces had retaken four neighbourhoods in the town of Al Mayadeen in Deir Ezzor province.
Last week, Daesh succeeded in expelling Syrian regime forces from Al Mayadeen two days after they entered the town.
The Syrian regime forces had recently described Mayadeen as the "military capital" of Daesh in Deir Ezzor.