Since Sunday, Russian planes have killed 69 civilians, among them 15 children, the watchdog said.
Meanwhile, the US-led coalition killed 12 people on Tuesday in strikes targeting other areas to the east of Deir al-Zour.
Most of the province of Deir al-Zour has been controlled by Islamic State since 2014.
Last week, forces loyal to Syrian President Bashar al-Assad broke the nearly three-year siege of the province's capital city of the same name.
On Saturday, a Syrian Kurd-led alliance, supported by the United States, started a separate offensive against Islamic State in the province.
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Meanwhile, the US-led coalition killed 12 people on Tuesday in strikes targeting other areas to the east of Deir al-Zour.
Most of the province of Deir al-Zour has been controlled by Islamic State since 2014.
Last week, forces loyal to Syrian President Bashar al-Assad broke the nearly three-year siege of the province's capital city of the same name.
On Saturday, a Syrian Kurd-led alliance, supported by the United States, started a separate offensive against Islamic State in the province.
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