Syrian Observatory for Human Rights say civilians, including three children, were fleeing the village of Mahkan, south of Al Mayadeen city.
Russian air strikes killed at least 14 civilians as they were crossing the Euphrates river near the militant-held town of Al Mayadeen in eastern Syria, the Syrian Observatory for Human Rights (SOHR) said on Friday.
"They were crossing the river on makeshift rafts in a village south of Mayadeen," SOHR 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 militants across the country.
Abdel Rahman said the civilians were fleeing the village of Mahkan, south of Al Mayadeen, which lies about 420 km east of Damascus and is one of the Daesh's main remaining bastions.
Al 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 this week advanced to within five km of the town.
Poised for Al Mayadeen
A military media unit run by the Lebanese Hezbollah group says regime forces and its allies gained control of positions and heights parallel to the main road linking Deir Ezzor and Al Mayadeen, located on the Euphrates in eastern Syria.
SOHR said the forces were only six km away from the city.
Daesh becomes 'virtual caliphate'
Experts and officials say Daesh's "virtual caliphate" could be hard to conquer.
The militant propaganda machine will continue to exist in hidden corners of the dark web, inciting sympathisers to action, they say.
"Defeating ISIL (Daesh) on the physical battlefield is not enough," General Joseph Votel, the top commander for US military forces in the Middle East, warned earlier this year.
"Following even a decisive defeat in Iraq and Syria, ISIL (Daesh) will likely retreat to a virtual safe haven, a virtual caliphate, from which it will continue to coordinate and inspire external attacks as well as build a support base until the group has the capability to reclaim physical territory."
He described this online network as "a distorted version of the historic Islamic caliphate: it is a stratified community of Muslims who are led by a caliph (currently Abu Bakr al Baghdadi), aspire to participate in a state governed by sharia, and are located in the global territory of cyberspace."
Under pressure from public authorities, internet providers and major online players are beginning to put in place measures and procedures to disrupt Daesh's exploitation of the web.