The strikes, the latest in a string of such incidents this week, targeted a group crossing the Euphrates near the jihadist-held town of Mayadeen, the Syrian Observatory for Human Rights said.
“They were crossing the river on makeshift rafts in a village south of Mayadeen,” Observatory director Rami Abdel Rahman said, adding that three children were among those killed overnight.
Russia has in recent days intensified its air raids in support of Syrian regime forces battling jihadists across the country.
Abdel Rahman said the civilians were fleeing the village of Mahkan, south of Mayadeen, which lies about 420 kilometers (260 miles) east of Damascus and is one of the Daesh group’s main remaining bastions.
Mayadeen has been under Daesh control since 2014 when the group swept across swathes of Iraq and Syria and proclaimed a “caliphate,” but regime forces have tightened the noose around the town.
The state news agency SANA said government forces advancing from desert areas northwest of Mayadeen had moved to within five kilometers (three miles) of the town.
In Deir Ezzor province, Daesh still controls Mayadeen, eastern neighborhoods of the city of Deir Ezzor further up the Euphrates Valley, the town of Albu Kamal downstream on the Iraqi border, and several other smaller towns.
Moscow has been carrying out relentless air strikes in support of its ally Damascus targeting both Daesh in Deir Ezzor province and rival jihadists led by Al-Qaeda’s former Syria affiliate in Idlib province in the northwest.
The Daesh group, which once controlled a territory roughly the size of Britain, has seen its “caliphate” shrink steadily over the past two years and has lost all but a few of its main hubs in both Iraq and Syria.
A Kurdish-led alliance is currently fighting Daesh in Raqqa, the group’s biggest bastion since the recapture by Iraqi forces of Mosul in July.
The city, further up the Euphrates, was the de facto Syrian capital of Daesh’s now collapsing “state.”
On Wednesday, a Russian air strike killed 38 civilians trying to flee the fighting in Deir Ezzor province, according to the Observatory.
The Observatory relies on a network of sources inside Syria and says it determines whose planes carry out raids according to type, location, flight patterns and munitions used.
The group has reported hundreds of civilians killed in operations against Daesh in Deir Ezzor and neighboring Raqqa province. On Tuesday, it said a US-led coalition strike in Raqqa killed at least 18 civilians.
Russia has not acknowledged any civilian deaths from its strikes since it intervened in Syria in 2015 and dismisses the Observatory’s reporting as biased.
On Thursday, the Red Cross said Syria was experiencing its worst levels of violence since the battle for second city Aleppo late last year.
“For the past two weeks, we have seen an increasingly worrying spike in military operations that correlates with high levels of civilian casualties,” Marianne Gasser, the head of the International Committee of the Red Cross delegation in Syria, said.